ALBERT

Description: This study focuses on the evaluation of teleseisms as estimators of long-period seismic site amplification in correspondence to large alluvial basins. Using the recordings of the 11 March 2011 M w  9.0 Tohoku-Oki, Japan, earthquake, the site response at low frequency of the Po Plain, Italy, was investigated. The interdistances among the analyzed sites, compared to the travel paths of the Tohoku-Oki waveforms with respect to the target area, allowed us to investigate the reliability of the standard spectral ratio (SSR) technique applied to teleseismic recordings. The results are presented as directional SSRs calculated considering 2 min of P , S , and Rayleigh ( LR ) waves, filtered from 0.025 to 1.0 Hz. Considering the horizontal components, at frequency from 0.04 to 0.3 Hz, the Po Plain stations show amplification factors up to 20 and 16, detected for the S and LR phases, respectively. In some cases, the amplified ground motion appeared to be affected by polarization phenomena, in particular in the north–south direction. Moving from the center to the edge of the basin, the LR -wave amplification remarkably decreases, in particular for frequencies between 0.1 and 0.3 Hz; this was not observed for the S wave. Amplification factors 〉10 were also detected for the vertical component, with increasing resonance periods moving from P to LR waves. Comparing SSRs with the single-station horizontal-to-vertical spectral ratios, the latter case shows that the vertical amplifications lead to the partial masking of the actual response of a site, in particular for frequencies 〉0.15 Hz. Finally, the relative P -wave amplitudes were also investigated. The results of the spectral analysis and the correlation between the relative P -wave amplitudes and the geometry of the bedrock suggest that the proposed approach is appropriate for the investigation of long-period seismic site response in similar settings.

Description: Near-fault pulse-like ground motions have long been known to be capable of inducing significant seismic damages to the building structures. Reasonable classification of such ground motions has been a challenge to earthquake engineers. This study serves to propose an energy-based approach that can be used to identify those ground motions with dominant pulses observed in the velocity time series; and time integral of the squared ground velocity is employed to represent the motion energy. For removing the influence of high-frequency contents, the potential velocity pulse is first extracted with a pulse model. The starting and ending time points as well as period of the velocity pulse are subsequently determined by the peak-point method. Records with peak ground velocities above 30 cm/s from a database containing more than 3600 recorded ground motions are selected and utilized to calibrate the final criterion. It is concluded that those ground motions whose dominant velocity pulses hold relative energy values of greater than 0.3 can be satisfactorily classified as pulse-like. The proposed approach is further used to identify pulse-like features in arbitrary orientations and pulse-like ground motions possibly caused by forward-directivity effects. Online Material: Tables identifying ground motions with near-fault pulse-like behavior.

Description: We studied the response spectral amplitudes and peak ground acceleration (PGA) of earthquakes with moment magnitude ( M ) from 3.0 to 6.0 to investigate regional differences in ground-motion amplitudes across North America on a nonparametric basis, for a common National Earthquake Hazards Reduction Program B/C site condition (e.g., shear-wave velocity of 760 m/s in the top 30 m of the soil column). We use southern California as the reference region because it has the most plentiful data against which to compare other regions. Amplitudes of response spectra in eastern Canada/northeastern United States become increasingly larger than those in southern California as distance, frequency, and magnitude increases. In the central United States, ground-motion amplitudes are larger than those in southern California at distances more than 100 km (and lower at distances less than 100 km), over all frequency and magnitude ranges studied. Amplitudes for crustal events in the Pacific Northwest/British Columbia are lower than those in southern California at frequencies ≥1 Hz, over all magnitude and distance ranges (but have similar amplitudes below 1 Hz). Amplitudes in northern California are similar to those in southern California at low frequencies (below 3.3 Hz) but have lower amplitudes at high frequencies (PGA) over all distances and magnitudes. We conclude that regional amplitude differences are largely attributable to complex frequency-dependent differences in regional attenuation. For example, the slope of apparent geometric spreading at distances less than 100 km is significantly steeper (more negative) in eastern Canada/northeastern United States than other regions and may be frequency dependent. The regional attributes of the attenuation comparisons appear to be the same for both vertical and horizontal components, at least for B/C site conditions. Online Material: Figures of region-dependent ground-motion amplitudes, apparent geometric spreading, statistical tests of the ground motions, and figures and table of ratios of ground motions relative to those from southern California.

Description: Defining the reference rock or soil condition related to ground-motion prediction is an important aspect of seismic-hazard analysis. In a previous study by the authors, a method was proposed to establish a reference rock profile for Switzerland through the comparison of empirical amplification functions with shear-wave velocity profiles at 27 selected sites of the Swiss National Seismic Network. The retrieved velocity profile served as reference for a regional ground-motion prediction equation. However, a lacking piece of information remained: the anelastic attenuation for such a reference profile. Reference attenuation is essential to correctly model and interpret amplification at high frequencies. In the present study we extended our approach to simultaneously model both the reference shear-wave velocity profile and the corresponding attenuation for Japan. We compared site-specific attenuation measurements with quarter-wavelength average velocities at 36 soil and rock sites from the Japanese KiK-net strong-motion network. The selected sites are characterized by a lack of observed resonance phenomena in order to avoid trade-off between amplification and attenuation effects. We establish a parametric model through regression analysis. The resulting model gives us the possibility to estimate anelastic attenuation of a rock site with a given velocity profile and provides the base for host-to-target adjustments of real or modeled ground motion.

Description: Geophysical measurements are often acquired at scattered locations in space. Therefore, interpolating or fitting the sparsely sampled data as a uniform function of space (a procedure commonly known as gridding) is a ubiquitous problem in geophysics. Most gridding methods require a model of spatial correlation for data. This spatial correlation model can often be inferred from some sort of secondary information, which may also be sparsely sampled in space. In this paper, we present a new method to model the geometry of a subducting slab in which we use a data-fitting approach to address the problem. Earthquakes and active-source seismic surveys provide estimates of depths of subducting slabs but only at scattered locations. In addition to estimates of depths from earthquake locations, focal mechanisms of subduction zone earthquakes also provide estimates of the strikes of the subducting slab on which they occur. We use these spatially sparse strike samples and the Earth’s curved surface geometry to infer a model for spatial correlation that guides a blended neighbor interpolation of slab depths. We then modify the interpolation method to account for the uncertainties associated with the depth estimates.

Description: Unusually severe structural damage was reported during the 2010 M  7.0 Haiti earthquake in the vicinity of Hotel Montana, located on top of a ridge in the district of Pétionville. Prompted by the observations, U.S. Geological Survey seismic stations were deployed, and aftershock recordings indicated ground-motion amplification on the top of the hill compared to adjacent stations on reference site conditions. The presence of topographic relief has been shown to significantly aggravate the consequences of strong ground motion during past events, and topographic effects were brought forward to explain the observations. In this paper, we test the hypothesis of topographic amplification as the dominant factor that contributed to the damage concentration in the vicinity of Hotel Montana. We initially conduct numerical simulations of the ridge seismic response assuming elastic homogeneous site conditions, and show that numerical predictions of topographic amplification disagree with the field data both in amplitude and in frequency. Conversely, while 1D ground-response analyses for the site conditions at the hilltop predict amplification in the same frequency range as the field data, they significantly underestimate the recorded amplitude. We then conduct numerical simulations of the foothill ridge response to seismic motion while accounting for soil layering, and qualitatively demonstrate that the recorded amplification is most likely attributed to coupled site–topographic amplification effects, namely to seismic waves trapped in the soft soil layers of the near surface, amplified as a consequence of reverberations, and further modified due to diffraction and scattering upon incidence on the irregular ground surface. Parametric investigations of the topography–soil amplification coupling effects are then conducted, and our results show that when accounting for a hypothetical soil–bedrock interface at 100 m depth, predictions are in excellent agreement with the observed motion.

Description: Shear-wave splitting (SWS) analysis using SKS , SKKS , and PKS (hereafter collectively called XKS ) phases is one of the most commonly used techniques in structural seismology. In spite of the apparent simplicity in performing SWS measurements, large discrepancies in published SWS parameters (fast direction and splitting time) suggest that a significant portion of splitting parameters has been incorrectly determined. Here, based on the popularly used minimization of transverse energy technique, we present a procedure that combines automatic data processing and careful manual screening, which includes adjusting the XKS window used for splitting analysis, modifying band-pass filtering corner frequencies, and verifying and (if necessary) changing the quality ranking of the measurements. Using real and synthetic data, we discuss causes and diagnostics of a number of common problems in performing SWS analysis, and suggest possible remedies. Those problems include noise in the XKS window being mistaken as signal, non- XKS seismic arrivals in the XKS window, excessive use of null ranking, measurements from misoriented sensors and from sensors with mechanical problems, and inappropriate dismissal of usable measurements.

Description: The energy flux F at the rupture tip has been previously computed only for 2D steady-state singular cracks. In this paper, I compute F for fully dynamic 3D ruptures, propagating both with constant and variable rupture speed ( v r ) over finite faults directed by a governing law with a cohesive zone (and thus nonsingular ruptures). The results presented here indicate that F is positive and increasing over the whole range of v r from zero up to P -wave speed. This is in contrast with 2D steady-state singular cracks, which predict the existence of a forbidden zone in the range of rupture speeds because in that interval F would be negative. Moreover, I found that in 3D ruptures with cohesive force, F is proportional to v r , again in contrast to 2D steady-state singular cracks, in which F is not a unique function of v r and also exhibits an inverse dependence on v r . More specifically, it emerges that fast earthquakes tend to have a higher energy flux at the crack tip compared with slow ruptures. Finally, I show that the magnitude of F is basically due to its component aligned in the direction of the initial shear stress.

Description: One approach to investigate earthquake source processes is to produce kinematic source models from inversion of seismic records and geodetic data. The setup of the inversion requires a variety of assumptions and constraints to restrict the range of possible models. Here, we evaluate to what extent physically plausible earthquake scenarios are reliably restituted in spite of these restrictions. We study which characteristics of ruptures, such as rupture velocity, slip distribution, stress drop, rise time, and slip function, can be reliably determined from the inversion of near-field seismic and geodetic data. Using spontaneous dynamic rupture simulations, we generate five earthquake scenarios, each of which has different characteristics of the source process. Then we conduct a blind test by modeling the synthetic near-source data using a standard inversion scheme that optimizes the fit to the observations while searching for solutions with minimum roughness. The inversion procedure assumes a rupture front propagating away from the hypocenter with variable rupture velocity and a simple cosine slip-time function. Our results show that, overall, slip distribution and stress drop are reasonably well determined even for input models with relatively complex histories (such as a subshear rupture transitioning to supershear speeds). Depth-averaged rupture velocities are also reasonably well resolved although their estimate progressively deteriorates away from the hypocenter. The local rise time and slip function are not well resolved, but there is some sensitivity to the rupture pulse width, which can be used to differentiate between pulse-like and crack-like ruptures. Our test for understanding the inaccuracies in Green’s functions shows that random 3D perturbations of 5% standard deviation do not lead to significant degradation of the estimation of earthquake source parameters. As remedies to the current limitations, we propose smoothing slip function parameters and using more complicated inversion schemes only if data necessitates them. Online Material: Figures showing snapshots of forward and inverse modeling of rupture, L curves, slip models, and waveform fits.

Description: Shear-wave velocity ( V S ) and time-averaged shear-wave velocity to 30 m depth ( V S 30 ) are the key parameters used in seismic site response modeling and earthquake engineering design. Where V S data are limited, available data are often used to develop and refine map-based proxy models of V S 30 for predicting ground-motion intensities. In this paper, we present shallow V S data from 27 sites in Puerto Rico. These data were acquired using a multimethod acquisition approach consisting of noninvasive, collocated, active-source body-wave (refraction/reflection), active-source surface wave at nine sites, and passive-source surface-wave refraction microtremor (ReMi) techniques. V S -versus-depth models are constructed and used to calculate spectral response plots for each site. Factors affecting method reliability are analyzed with respect to site-specific differences in bedrock V S and spectral response. At many but not all sites, body- and surface-wave methods generally determine similar depths to bedrock, and it is the difference in bedrock V S that influences site amplification. The predicted resonant frequencies for the majority of the sites are observed to be within a relatively narrow bandwidth of 1–3.5 Hz. For a first-order comparison of peak frequency position, predictive spectral response plots from eight sites are plotted along with seismograph instrument spectra derived from the time series of the 16 May 2010 Puerto Rico earthquake. We show how a multimethod acquisition approach using collocated arrays compliments and corroborates V S results, thus adding confidence that reliable site characterization information has been obtained.

Description: We have integrated waveform and arrival-onset data collected in Costa Rica as part of the National Science Foundation (NSF)-sponsored Costa Rica Seismogenic Zone Experiment (CRSEIZE) and along central Costa Rica and Nicaragua as part of the German SFB 574 program. The five arrays, composed of different sensor types (one- and three-component land and ocean bottom seismometers and hydrophones), were archived using different software packages (Antelope and SEISAN) and were automatically and manually picked using various quality criteria resulting in a disparate set of pick weights. We evaluate pick quality using automated arrival detection and picking algorithm based on the wavelet transform and Akaike information criterion picker. The consistency of the arrival information over various scales provides a basis for assigning a quality to the analyst pick. Approximately 31% of P arrival times and 26% of S times have been classified as high-quality picks (quality 0–1). An additional 21% of P times and 27% of S arrivals are good quality (quality 2–3). The revised quality picks are mapped directly into new pick weights for inversion studies. We explore the effect of new weighting and removal of poor data by relocating hypocenters through a minimum 1D velocity model and conducting double-difference local earthquake tomography (LET). Analysis of the hypocenter relocation and seismic velocity tomography results suggest that using the improved quality determinations have a greater effect on improving sharpness in the velocity images than on the magnitude of hypocentral movement. Online Material: Figures of waveforms, event statistics, and tomography; and tables of station and event parameters, station qualities, velocity model, and hypocentral parameters.

Description: Because of the socioeconomic environment in the small island nation of Haiti, no seismic recording stations were operating in the source region at the time of the 2010 M w  7.0 earthquake. The lack of strong motion instruments has hindered the estimation of the amplitude, duration, and frequency content of the ground shaking caused by the seismic event. In this study, synthetic broadband strong ground motions are generated in the vicinity of the 2010 Haiti earthquake. The low-frequency components of the synthetic motions are simulated using a slip model compatible with seismological observations, geologic field data, and space geodetic measurements. The computations are carried out using the discrete wavenumber representation method and the generalized transmission and reflection coefficient technique. The high-frequency ground-motion components are generated using the stochastic modeling approach and the specific barrier model. The two independently derived ground-motion components are subsequently combined using matched filtering at a crossover frequency of 1 Hz to generate broadband ground-motion time histories and response spectra for the city of Port-au-Prince and other sites in the vicinity of the earthquake. Finally, the synthetic strong ground motions are compared against peak ground-motion estimates inferred from the U.S. Geologic Survey ShakeMap of peak ground accelerations, ground-motion prediction equations, and observed structural damage. The synthetic time histories and response spectra generated in this study should be seen as plausible, but not necessarily unique, ground motions that capture the primary features of the 2010 Haiti earthquake.

Description: I present a new 3D seismic velocity model and high-precision earthquake relocations between 1981 and 2010 near the Salton Trough and the San Jacinto fault zone. The simul2000 tomography algorithm is applied to derive the 3D V P and V P / V S models using first arrivals of a composite event data set. The final V P model correlates with geological features at shallow depths and is more consistent with the refraction studies than the starting 3D regional-scale model. The V P / V S model shows strong variations in the upper crust and is dominated by relatively low values (below 1.7) in the middle crust except for the Salton Trough and the Imperial Valley. The newly resolved model is used to relocate all the seismicity in the study area. I then apply the similar-event cluster analysis and differential-time relocation approach based on waveform cross-correlation data to the 3D relocated events. A dramatic sharpening of seismicity patterns is obtained after using these methods. The new locations are more tightly clustered than the previous catalogs mainly due to the different absolute locations. The depth distribution along a basal surface may suggest the existence of a detachment fault from the north end of the Salton Trough to United States–Mexico border. The fine-scale velocity structure and precise earthquake relocations will be helpful for investigating the fault geometry, seismicity, stress interaction, and other seismological studies for southern California. Online Material: Figures of model resolution tests, cross-sectional comparisons of different P -velocity models, and earthquake depth distributions.

Description: Recent parallel development of improved quantitative methods to analyze intensity distributions for historical earthquakes and of web-based systems for collecting intensity data for modern earthquakes provides an opportunity to reconsider not only important individual historical earthquakes but also the overall characterization of intensity distributions for historical events. The focus of this study is a comparison between intensity distributions of historical earthquakes with those from modern earthquakes for which intensities have been determined by the U.S. Geological Survey "Did You Feel It?" (DYFI) website (see Data and Resources ). As an example of a historical earthquake, I focus initially on the 1843 Marked Tree, Arkansas, event. Its magnitude has been previously estimated as 6.0–6.2. I first reevaluate the macroseismic effects of this earthquake, assigning intensities using a traditional approach, and estimate a preferred magnitude of 5.4. Modified Mercalli intensity (MMI) values for the Marked Tree earthquake are higher, on average, than those from the 2011 M w  5.8 Mineral, Virginia, earthquake for distances ≤500 km but comparable or lower on average at larger distances, with a smaller overall felt extent. Intensity distributions for other moderate historical earthquakes reveal similar discrepancies; the discrepancy is also even more pronounced using earlier published intensities for the 1843 earthquake. I discuss several hypotheses to explain the discrepancies, including the possibility that intensity values associated with historical earthquakes are commonly inflated due to reporting/sampling biases. A detailed consideration of the DYFI intensity distribution for the Mineral earthquake illustrates how reporting and sampling biases can account for historical earthquake intensity biases as high as two intensity units and for the qualitative difference in intensity distance decays for modern versus historical events. Thus, intensity maps for historical earthquakes tend to imply more widespread damage patterns than are revealed by intensity distributions of modern earthquakes of comparable magnitude. However, intensity accounts of historical earthquakes often include fragmentary accounts suggesting long-period shaking effects that will likely not be captured fully in historical intensity distributions. Online Material: Archival accounts for the 4 January 1843 Marked Tree, Arkansas, and 8 October 1857 Southern Illinois earthquakes.

Description: A catalog for earthquakes that occurred in western Turkey during the period 1964–2010 is compiled for achieving homogeneity for magnitudes. Data are obtained from the International Seismological Center (ISC), where earthquake magnitudes are reported in different scales and come from a variety of sources. For establishing a common magnitude expression, namely an equivalent moment magnitude , new relations correlating the different magnitude scales with each other are derived from converting as many as possible of the magnitudes reported in the ISC bulletins. After magnitude conversions, the completeness magnitude M c is sought by modifying the goodness-of-fit method of Wiemer and Wyss (2000) to become more appropriate for datasets with smaller sample size and higher M c thresholds. The study region is divided into four smaller regions on the basis of spatial data homogeneity, while different periods of similar seismic network performance are recognized and tested to seek spatiotemporal variation of M c . The results derived in each case are compared with those yielded by the application of both the original goodness-of-fit and maximum curvature methods and are found to be quite similar, although there are still cases with a difference exceeding 0.3 magnitude units. The goodness-of-fit method is very sensitive in the selection of the desirable percentage of fitting a power law (90% or 95%), whereas the proposed modification makes it independent of this level selection, and performing better especially for datasets that include events before 1990, when higher completeness magnitudes are evident. Online Material: Earthquake catalog with equivalent moment magnitude for western Turkey.

Description: Characterizing surface deformation throughout a full earthquake cycle is a challenge due to the lack of high-resolution geodetic observations of duration comparable to that of characteristic earthquake recurrence intervals (250–10,000 years). Here we approach this problem by comparing long-term geologic slip rates with geodetically derived fault slip rates by sampling only a short fraction (0.001%–0.1%) of a complete earthquake cycle along 15 continental strike-slip faults. Geodetic observations provide snapshots of surface deformation from different times through the earthquake cycle. The timing of the last earthquake on many of these faults is poorly known, and may vary greatly from fault to fault. Assuming that the underlying mechanics of the seismic cycle are similar for all faults, geodetic observations from different faults may be interpreted as samples over a significantly larger fraction of the earthquake cycle than could be obtained from the geodetic record along any one fault alone. As an ensemble, we find that geologically and geodetically inferred slip rates agree well with a linear relation of 0.94±0.09. To simultaneously explain both the ensemble agreement between geologic and geodetic slip-rate estimates with observations of rapid postseismic deformation, we consider the predictions from simple two-layer earthquake-cycle models with both Maxwell and Burgers viscoelastic rheologies. We find that a two-layer Burgers model, with two relaxation timescales, is consistent with observations of deformation throughout the earthquake cycle, whereas the widely used two-layer Maxwell model with a single relaxation timescale, is not, suggesting that the earthquake cycle is effectively characterized by a largely stress-recoverable rapid postseismic stage and a much more slowly varying interseismic stage.

Description: The largest earthquake in northern Illinois is the m b ~5.2 so-called "Aurora" earthquake of 26 May 1909. Reports from nearly 500 newspapers yielded intensities for about 400 localities published in the days following the earthquake and indicate that many damage reports (especially in Bloomington, Kenosha, Platteville, and Aurora) were not as severe as previously interpreted. Some early wire reports of damage were exaggerated and later retracted, or were not supported by local newspapers. Conversely, some local accounts of extensive damage (e.g., at Morris, Illinois) were not widely reported by syndicated news media. The felt area extends further than that of previous studies—from the Ohio River to northern Wisconsin, and from Lansing, Michigan, to near Cedar Rapids, Iowa. The felt area centers near Sandwich, Illinois; the highest intensity, VII, is assigned to Morris, Illinois. The event was felt over an area of 350,000–400,000 km 2 within a maximum radius of approximately 420 km. The distribution of felt area and intensity is similar to the m b  4.2 northern Illinois earthquake (28 June 2004), which has an instrumental epicenter near LaSalle, suggesting that the two events occurred in relatively close proximity. Our preferred epicenter for the 1909 event is near Sandwich, Illinois, based on intensity reports, and is located near the Sandwich fault, as is a potential small aftershock. This places the 1909 event into a tectonic framework and slightly further from the Chicago metropolitan area than previously proposed. Online Material: Tables of intensity reports, a list of newspapers from which intensity reports were extracted, and details of analog records and bulletins.

Description: The rate of M L ≥3 earthquakes in the central and eastern United States increased beginning in 2009, particularly in Oklahoma and central Arkansas, where fluid injection has occurred. We find evidence that suggests these rate increases are man-made by examining the rate changes in a catalog of M L ≥3 earthquakes in Oklahoma, which had a low background seismicity rate before 2009, as well as rate changes in a catalog of M L ≥2.2 earthquakes in central Arkansas, which had a history of earthquake swarms prior to the start of injection in 2009. In both cases, stochastic epidemic-type aftershock sequence models and statistical tests demonstrate that the earthquake rate change is statistically significant, and both the background rate of independent earthquakes and the aftershock productivity must increase in 2009 to explain the observed increase in seismicity. This suggests that a significant change in the underlying triggering process occurred. Both parameters vary, even when comparing natural to potentially induced swarms in Arkansas, which suggests that changes in both the background rate and the aftershock productivity may provide a way to distinguish man-made from natural earthquake rate changes. In Arkansas we also compare earthquake and injection well locations, finding that earthquakes within 6 km of an active injection well tend to occur closer together than those that occur before, after, or far from active injection. Thus, like a change in productivity, a change in interevent distance distribution may also be an indicator of induced seismicity.

Description: The earthquake source mechanism (description of the geometry of the source and its strength in terms of forces equivalent to rupturing of the rock mass) is routinely modeled as a moment tensor (MT) describing the earthquake focus as a point. However, sometimes this approximation is not satisfied, and seismic radiation keeps the directivity due to the finite extent of the source. Inversion into the MT then may yield a biased mechanism. Synthetic study in the Adamová and Síleny (2010) demonstrated the appearance of spurious non-double-couple components in the mechanism even for a pure double-couple (DC) source. Their method was designed to reduce the spurious source components by using the second-degree moments to evaluate their contribution into the records and subtract it from the data. Here we applied the procedure to five moderate to large regional events with large nonshear components. They are mostly located on large tectonic faults where predominantly pure shear slip is expected. We studied one event on the prominent North Anatolian fault, three events in the Pacific area, and one event in Bolivia. In most cases, the non-DC components essentially were reduced, and the geometry of the mechanism remained largely unchanged. This confirms the hypothesis that part of the non-DC components in regional MT solutions may be spurious due to the neglect of the source finiteness in the routine procedure of the MT retrieval. In addition, the geometrical and kinematical characteristics of the foci provided by the second-degree moments (the source ellipsoid and rupture velocity vector) are mostly consistent with the fault geometry, aftershock distribution, and estimates of rupture speed from available previous studies.

Description: Seismic-hazard assessment for earthquakes with long recurrence intervals requires long earthquake records. Historical records for seismic damage can complement instrumental earthquake records, which is particularly useful for low-seismicity regions. Uncertainty in epicenters and magnitudes, however, hinders the full use of historical earthquake records. A probabilistic method to determine the epicenters of historical events is presented. The epicenters of historical events are determined probabilistically considering the nature of seismicity such that the spatial distribution of seismicity is nearly stationary with time in a constant tectonic environment. The probabilities for historical events to have occurred at given locations can be calculated using an instrumental seismicity density function and a distance-dependent weighting function. A location is selected randomly from a set of candidate source locations, of which probabilities are greater than a given prescribed value. The epicentral seismic intensity for the determined source location is calculated using an intensity–distance relationship. The magnitude is determined using an intensity–magnitude relationship. The method is verified with analysis of seismic intensity data for earthquakes in California. The method is applied to an ~1900 year long Korean historical seismic record, and the magnitudes of historical earthquakes are estimated. The Gutenberg–Richter b values for the historical events are determined to be 0.73. It is observed that the northwestern and southern peninsula, and the southeastern offshore region have high seismic-hazard potentials.

Description: Yield estimation of small explosions at local distances represents a challenge for the nuclear explosion monitoring community. We have examined the feasibility of using short-period surface-wave magnitudes, called , to estimate explosion yields at local distances (〈100 km). We have modified the Russell (2006) M s formula, which was derived for periods of 8–25 s for distances beyond 50 km, for application at local distances and 1 s period. We have studied short-period surface-wave attenuation in diverse lithologies in order to incorporate an attenuation term in the magnitude scale, which is suitable for . We have also incorporated multiple excitation corrections for based on the near-source seismic velocities, which greatly affect the source-region amplitudes for . It is important to note that in the formula the excitation is estimated from the measured group velocity. We have also derived a new Butterworth filter cutout definition for filtering near 1 s period at distances between 2 and 100 km. We used the new formula to estimate for 39 small (37≤ Y ≤12,270 kg TNT equivalent) and shallow (〈120 m) explosions detonated in North America in lithologies ranging from alluvium to granite. Regressions of the magnitudes with yield result in the equation for chemical explosions with Y 〈12,270 kg. An F factor with 95% confidence was determined to be 2.25, giving lower and upper bounds on the yield estimates of Y /2.25 and Y x 2.25, respectively. We applied the relationship (assuming factor of 2 equivalence between chemical and nuclear) to nuclear explosions detonated at the Degelen and Shagan, Kazakhstan, test sites. The estimated yields based on magnitudes were often within 20% of the true yield and had smaller F factor than the estimated yields for United States chemical explosions. Online Material: Tables of event information and estimates.

Description: Co- and postseismic slip of the great earthquakes can give rise to temporal changes in the medium either due to strong ground motion damaging near-surface sediment layer or stress perturbations modulating crack density and/or fluid movement at depth. Such time-varying crustal properties can result in fractional change in seismic velocity that can be probed from cross-correlating waveforms and measuring their time lags within a repeating earthquake sequence. This study analyzes lag times of high-frequency (0.5–2.0 Hz) P - and S -coda waves as well as long-period (0.03–0.1 Hz) surface waves from repeating aftershock sequences of the great 2004 Sumatra–Andaman and 2005 Nias–Simeulue earthquakes. The observed lag times reveal several major characteristics: (1) lag-time series ( t ) of S coda for the 2004 sequences fluctuate around zero and are sometimes negative as a function of lapse time, whereas ( t ) of S coda for the 2005 sequences exhibit a monotonic increase as a function of lapse time; (2) average velocity reduction of S coda (– V S ) is about two times larger than that of P coda (– V P ); average velocity reduction of Rayleigh waves (– V LR ) is 3–4 times larger than that of Love waves (– V LQ ); and (3)  V S and V LR display temporal velocity recovery with calendar time, especially for the 2005 sequences. The form of temporal velocity recovery of V S of the 2005 sequences is similar to available displacement time series of the nearby geodetic station. Whereas we discuss potential artifacts, such as source separation, temporal changes of the noise field, and instrument response, observations collectively point to nonuniform temporal velocity reduction in the crust modulated by co- or/and postseismic slip of the 2004/2005 great earthquakes. Online Material: Table of source parameters and figure showing tests on lag-time measurements of long-period Rayleigh waves.

Description: This study applies Bayesian inversion to receiver functions (RFs) to estimate local shear-wave velocity ( V S ) structure of the Juan de Fuca (JdF) plate beneath the northern Cascadia subduction zone (CSZ) offshore and onshore Vancouver Island, British Columbia, Canada. We use passive seismic data recorded on NEPTUNE (NorthEast Pacific Time-series Undersea Networked Experiments) Canada ocean-bottom seismometers (OBSs), on temporary autonomous KECK Foundation OBSs, and on two land-based seismometers on Vancouver Island that are part of the Canadian National Seismograph Network (CNSN). Three-component, broadband recordings of large ( ), distant (30°–100°) earthquakes are used to compute RFs dominated by locally generated P -to- S converted waves. These are subsequently inverted using a nonlinear Bayesian approach that yields optimal profiles of V S , V P (compressional-wave velocity), and strike and dip angles, as well as quantitative uncertainty estimates for these parameters. The introduction of NEPTUNE Canada helps fill a gap in offshore seismic monitoring. Results from OBS stations indicate a thin oceanic crust at the JdF Ridge which thickens to ~10 km at the continental slope where sediment thickness also increases to ~5 km. At OZB, a coastal station, a 6–8 km thick, two-part low-velocity zone (LVZ) is imaged at 19 km depth. An LVZ of similar thickness is also observed 34 km beneath PGC, a south-central Vancouver Island station. The thickness of the LVZ imaged at these two land-based stations indicates that the oceanic sediments are not subducted but are scraped off the JdF plate and accreted to the North American plate. Determining these V S models at various stages of the CSZ provides a more detailed image of the subducting plate, and therefore contributes valuable new information useful for seismic-hazard analysis.

Description: We have developed a new local magnitude scale M L for the United Kingdom (UK) to replace the Hutton and Boore (1987) scale developed for southern California, which has been used in the UK until now. The new UK scale is developed from 1482 observations of 85 earthquakes on 50 stations located across the British Isles and Ireland. Most of the observations are from epicentral distances of less than 600 km and only few from greater distances up to 900 km. The distance range of the scale is, therefore, 0–600 km. The amplitude observations were used to invert for the parameters defining distance dependence in the M L scale and station corrections. Synthetic tests showed that the inversion was robust. The new M L scale for the UK is given by M L =log A +0.95log R +0.00183 R –1.76, in which A is horizontal-component ground displacement amplitude in nanometers. The amplitudes are measured on traces that are filtered to simulate the Wood–Anderson seismograph. R is the hypocentral distance (in km). The UK scale is intermediate between scales determined for California and those of other intraplate areas such as Norway or the northeastern United States. The absolute station corrections found are all less than 0.5. The scale derived for the UK helps to reduce the overall variance of the mean magnitude estimates by 30%. Much of this improvement is due to the use of station corrections. Applying the UK scale to the database of recorded earthquakes results in a reduction of magnitude for earthquakes above M L  2 and a slight increase in magnitude for earthquakes below M L  2. The biggest change to the M L computation is likely to be for small earthquakes with few amplitude readings, where the use of station corrections makes a significant difference.

Description: We characterize shallow subsurface faulting and basin structure along a transect through heavily urbanized Reno, Nevada, with high-resolution seismic reflection imaging. The 6.8 km of P -wave data image the subsurface to approximately 800 m depth and delineate two subbasins and basin uplift that are consistent with structure previously inferred from gravity modeling in this region of the northern Walker Lane. We interpret two primary faults that bound the uplift and deform Quaternary deposits. The dip of Quaternary and Tertiary strata in the western subbasin increases with greater depth to the east, suggesting recurrent fault motion across the westernmost of these faults. Deformation in the Quaternary section of the western subbasin is likely evidence of extensional growth folding at the edge of the Truckee River through Reno. This deformation is north of, and on trend with, previously mapped Quaternary fault strands of the Mt. Rose fault zone. In addition to corroborating the existence of previously inferred intrabasin structure, these data provide evidence for an active extensional Quaternary fault at a previously unknown location within the Truckee Meadows basin that furthers our understanding of both the seismotectonic framework and earthquake hazards in this urbanized region.

Description: We investigate coseismic deformation of the 24 March 2011 M w  6.8 Tarlay, Myanmar, earthquake using ALOS PALSAR data from both descending and ascending passes. Using high-quality synthetic aperture radar interferograms and amplitude-offset images, the nearly linear surface rupture is well traced along the western end of the Nam Ma fault and strikes ~69°. From both descending and ascending pass Interferometric Synthetic Aperture Radar data and a rigorous maximum a posteriori probabilistic inversion method, we infer that the event involved mostly a pure left-lateral strike-slip rupture with near-vertical geometry. Our one-segment model shows that the maximum slip of ~4.1 m occurred at ~4 km depth, much larger than the slip at the surface. Both interferograms also reveal a small segment to the east of the main rupture, in a densely populated farming area. Our inversion of a two-segment model shows a similar slip distribution on the main fault, in addition to ~0.1–0.3 m left-lateral slip with normal component on a 58° north-dipping segment. The total seismic moment from the two-segment model is 1.95 x 10 19 N·m, equivalent to an M w  6.79 earthquake, which is comparable to the U.S. Geological Survey seismic inversion estimate of 2.10 x 10 19 N·m ( M w  6.84). The earthquake occurred within a group of east-northeast-striking left-lateral strike-slip faults near the Myanmar–Laos border, which are seismically active and reflect a system of actively clockwise rotating blocks. Online Material: Figures of InSAR observations, amplitude-offset maps, InSAR deformation decomposition, one segment model inversion residuals, single data set inversion results, and tectonic setting.

Description: In probabilistic seismic-hazard analysis, epistemic uncertainties are commonly treated within a logic-tree framework in which the branch weights express the degree of belief of an expert in a set of models. For the calculation of the distribution of hazard curves, these branch weights represent subjective probabilities. A major challenge for experts is to provide logically consistent weight estimates (in the sense of Kolmogorovs axioms), to be aware of the multitude of heuristics, and to minimize the biases which affect human judgment under uncertainty. We introduce a platform-independent, interactive program enabling us to quantify, elicit, and transfer expert knowledge into a set of subjective probabilities by applying experimental design theory, following the approach of Curtis and Wood (2004) . Instead of determining the set of probabilities for all models in a single step, the computer-driven elicitation process is performed as a sequence of evaluations of relative weights for small subsets of models. From these, the probabilities for the whole model set are determined as a solution of an optimization problem. The result of this process is a set of logically consistent probabilities together with a measure of confidence determined from the amount of conflicting information which is provided by the expert during the relative weighting process. We experiment with different scenarios simulating likely expert behaviors in the context of knowledge elicitation and show the impact this has on the results. The overall aim is to provide a smart elicitation technique, and our findings serve as a guide for practical applications. Online Material: Interactive software for the elicitation of expert knowledge.

Description: Seismic spectral models for chemical and nuclear explosions are used in many applications including network modeling and yield estimation. Here we compare the models presented in Denny and Johnson (1991) and Mueller and Murphy (1971) with each other and with new results from the Source Physics Experiments (SPE). We demonstrate analytically the two models are in substantial agreement for large and normally buried explosions, consistent with much of the historic data collected during American and Soviet nuclear testing. However, for small and/or deeply buried explosions, the spectral predictions of the two models can differ significantly. For example, the predicted yield of a 1 km deep, M w  2 nuclear explosion differs by more than a factor of 5; and, for the same moment and depth chemical explosion, the difference is greater than a factor of 10. We compare the models with initial data from the SPE, which include small and overburied chemical explosions. The corner frequency of the one-ton SPE explosion (SPE-2) is slightly higher than the Mueller and Murphy (1971) model and approximately double the Denny and Johnson (1991) model prediction. The absolute moment of the one-tenth ton SPE explosion (SPE-1) is near the Denny and Johnson (1991) prediction and an order of magnitude smaller than the Mueller and Murphy (1971) prediction. The low-frequency moment ratio for SPE-2/SPE-1 is more consistent with the Denny and Johnson (1991) model. The results presented here show the need for an improved explosion source model that can accommodate a wider range of yields and emplacement conditions. Online Material: Moment magnitude, corner frequency, and yield for all geologic media.

Description: Northeast India has been subjected to extensive compressional forces, mainly in north–south and east–west directions resulting from the convergence of the Indian plate with the Eurasian and Burmese plates, respectively. The area is characterized as one of the most seismically active regions of the world; however, the lower Assam valley’s microseismicity has not been monitored and studied intensively by a dense seismic network during the past. During this study, a seismic network of 76 stations was deployed in northeastern India for one year. Hundreds of microearthquakes were recorded. The most accurately located events, moment tensor solutions, and focal mechanisms were used in order to define the seismotectonic and stress regime in the area.

Description: Destructive earthquakes occur unexpectedly: although evident everywhere to everybody and essentially tied to earthquake inherent unpredictability, this issue appears difficult to formalize. One formalization is developed here in terms of event recurrence. The problem is cast in statistical terms using reverse queue theory, and the solution applied to a uniquely detailed database of seismogenic sources: the DISS Italian database. As a result, the series of the recurrence times estimated from palaeoseismology and geology is found to be statistically incompatible with the series of the time intervals elapsed since last events. Such an incompatibility stands for a number of active seismogenic sources one order of magnitude larger than the number of sources which produced historic and instrumental earthquakes. In practice, this implies that only 1 of the 10 future M w ≥5.5 earthquakes will be a recurrence of an event reported in the Italian seismic catalogs. This has radical consequences on seismic-hazard estimates.

Description: Once assumed to be locked, we show that the northern third of the Greenville fault (GF) creeps at 2 mm/yr, based on 47 yr of trilateration net data. This northern GF creep rate equals its 11 ka slip rate, suggesting a low strain accumulation rate. In 1980, the GF, easternmost strand of the San Andreas fault system east of San Francisco Bay, produced an M w  5.8 earthquake with a 6 km surface rupture and dextral slip growing to ≥2 cm on cracks over a few weeks. Trilateration shows a 10 cm post-1980 transient slip ending in 1984. Analysis of 2000–2012 crustal velocities on continuous Global Positioning System stations, allows creep rates of ~2 mm/yr on the northern GF, 0–1 mm/yr on the central GF, and ~0 mm/yr on its southern third. Modeled depth ranges of creep along the GF allow 5%–25% aseismic release. Greater locking in the southern two-thirds of the GF is consistent with paleoseismic evidence there for large late Holocene ruptures. Because the GF lacks large (〉1 km) discontinuities likely to arrest higher (~1 m) slip ruptures, we expect full-length (54 km) ruptures to occur that include the northern creeping zone. We estimate sufficient strain accumulation on the entire GF to produce M w  6.9 earthquakes with a mean recurrence of ~575 yr. While the creeping 16 km northern part has the potential to produce an M w  6.2 event in 240 yr, it may rupture in both moderate (1980) and large events. These two-dimensional-model estimates of creep rate along the southern GF need verification with small aperture surveys. Online Material: Green net data file.

Description: At the present time, micro-electro-mechanical system (MEMS) accelerometers seem to provide adequate sensitivity, noise level, and dynamic range to be applicable to earthquake strong-motion acquisition. The current common use of MEMS accelerometers in the modern mobile phone may provide a new means to easily enormously increase the number of observations when a strong earthquake occurs. However, before utilizing the signals recorded by a device, like a mobile phone equipped with a low-cost three-axis MEMS accelerometer for any scientific purpose, it is important to verify that the signal collected provides reliable records of ground motion. In this paper, we have tested the LIS331DLH MEMS accelerometer installed in the iPhone mobile phone using a vibrating table and the EpiSensor FBA (force-balance accelerometer) ES-T as the reference sensor. Our tests show that, in the typical frequency and amplitude range of interest of earthquake engineering (0.2–20 Hz and , in which is the standard gravity of acceleration, or ), the LIS331DLH MEMS accelerometer has excellent frequency and phase response, comparable with that of some standard FBAs produced for strong-motion seismology. The main drawback of the LIS331DLH MEMS accelerometer is its low sensitivity, due to the high level of instrumental self noise, and so it can be used effectively only to record moderate to strong earthquakes ( M L 〉5) near the epicentral area.

Description: Optimizing a seismic network for locating earthquakes is a crucial issue in seismology. Precise earthquake location is the key factor for most sophisticated seismological analyses and for the monitoring of tectonic and volcanic areas. Network testing and optimization should therefore be a basic procedure to plan, install, and improve a monitoring seismic network. Here, we evaluate the most appropriate methods for network testing, using two approaches based on linearized and Bayesian methods. We then propose a new procedure for seismic network optimization, based on the direct comparison of all the possible networks resulting from the permutation of M stations in N sites (with N 〉 M ). The performance of a network can be defined using different criteria. In addition to the covariance matrix as conventionally applied, we have introduced the condition number of the coefficient matrix. Our new procedure is very efficient for network optimization with respect to multiple criteria and overcomes several problems of current procedures. Applied to the Campi Flegrei volcanic area, the method has identified a key configuration for optimizing and improving the seismic-monitoring network.

Description: Among scoring methods employed to determine the performance of probability predictions, the log-likelihood method is the most common and useful. Although the log-likelihood score evaluates the comprehensive power of forecasts, we need to further evaluate the topical predictive powers of respective factors of seismicity, such as total numbers, occurrence times, locations, and magnitudes. For this purpose, we used the conditional- or marginal-likelihood function based on the observed events. Such topical scores reveal both strengths and weaknesses of a forecasting model and suggest the necessary improvements. We applied these scores to the probability forecasts during the devastating period of March 2011, during which the M w  9.0 Off the Pacific Coast of Tohoku-Oki earthquake struck. However, the evaluations did not suggest that any of the prospective forecast models were consistently satisfactory. Hence, we undertook two additional types of retrospective forecasting experiments to investigate the reasons, including the possibility that the seismicity rate pattern has changed after the M  9 mega-earthquake. In addition, our experiments revealed a technical difficulty in the one-day forecasting protocol adopted by the Collaboratory for the Study of Earthquake Predictability (CSEP). Results of further experiments lead us to recommend specific modifications to the CSEP protocols, leading to real-time forecasts and their evaluations.

Description: The societal importance and implications of seismic-hazard assessment forces the scientific community to pay increasing attention to the evaluation of uncertainty in order to provide accurate assessments. Probabilistic seismic hazard assessment (PSHA) formally accounts for the natural variability of the involved phenomena, from seismic sources to wave propagation. Recently, increased attention has been paid to the consequences of alternative modeling procedures on hazard results. This uncertainty, essentially of epistemic nature, has been shown to have major impacts on PSHA results, leading to extensive applications of techniques like the logic tree. Here, we develop a formal Bayesian inference scheme for PSHA that allows us, on the one hand, to explicitly account for all uncertainties and, on the other hand, to consider a larger set of sources of information, from heterogeneous models to past data. This process decreases the chance of undesirable biases and leads to a controlled increase of the precision of the probabilistic assessment. In addition, the proposed Bayesian scheme allows (1) the assignment of a subjective reliability to single models, without requirement of completeness or homogeneity, and (2) a transparent and uniform evaluation of the strength of each piece of information used on the final results. The applicability of the method is demonstrated through the assessment of seismic hazard in the Emilia–Romagna region of northern Italy. In this application the results of a traditional Cornell–McGuire hazard model based on a logic tree are updated with the historical macroseismic records to provide a unified assessment that accounts for both sources of information.

Description: The epidemic-type aftershock sequence (ETAS) model has been shown to describe successfully the statistical seismicity properties, if earthquake triggering is related to tectonic forcing and earthquake-induced stress changes. However, seismicity is locally often dominated by stress changes related to transient aseismic processes. To avoid erroneous parameter estimations leading to biased forecasts, it is important to account for those transients. We apply a recently developed iterative algorithm based on the ETAS model to identify the time-dependent background and ETAS parameters simultaneously. We find that this procedure works well for synthetic data sets if catalog errors are appropriately considered. However, ignoring the time dependence leads to significantly biased parameter estimations. In particular, the α -value describing the magnitude dependence of the triggering kernel can be strongly underestimated if transients are ignored. Low α -values have been previously found for swarm activity, for which transient aseismic processes are expected to play a major role. These observed anomalously low α -values might thus indicate the importance of transient forcing, rather than being due to differences in the earthquake–earthquake trigger mechanism. To explore this, we apply the procedure systematically to earthquake clusters detected in southern California and to earthquake swarm activity in Vogtland/Western Bohemia. While low α -values are mostly shown to be a consequence of catalog errors and time-dependent forcing but not related to different earthquake–earthquake interaction mechanisms, some significant low values are observed in high heat-flow areas in California, confirming the existence of thermal control on earthquake triggering.

Description: In January 2011, a sequence of earthquakes occurred in close proximity to a well, which was being hydraulically fractured in south-central Oklahoma. The hydraulic fracturing of the Picket Unit B Well 4–18 occurred from 16 January 2011 18:43 through 22 January 16:54 UTC. This vertical well penetrated into the mature Eola-Robberson oil field. Earthquakes were identified by cross correlating template waveforms from manually identified earthquakes and cross correlating these templates through the entire operation period of the Earthscope USArray Transportable Array (TA) station X34A. This produced a series of 116 earthquakes, which occurred from 17 January 2011 19:06 through 23 January 3:13 UTC with no other similar earthquakes identified at other times prior to or post-hydraulic fracturing. The identified earthquakes range in local magnitude ( M L ) from 0.6 to 2.9, with 16 earthquakes M L  2 or greater and a b -value of 0.98. There is a strong temporal correlation between hydraulic fracturing and earthquakes. This correlation is strengthened because hydraulic fracturing operations ceased for ~2 days due to bad weather, and earthquakes can be observed to cease during this period and resume after hydraulic fracturing had resumed. Earthquakes were relocated using cross-correlated phase arrivals and bootstrap iterations of hypoDD. Locations were well constrained for 86 earthquakes. These earthquake locations clearly delineate a fault which strikes ~166°, subparallel to the mapped minor fault sets in the area, and dips steeply to the west. The earthquakes appear to have occurred at shallow depths from ~2 to 3 km and within ~2.5 km horizontally of the well. The first earthquake occurred ~24 hrs after hydraulic fracturing began at the well. This delay is consistent with the diffusion of pore pressure in the subsurface over a distance of ~2 km. Online Material: Results from bootstrap hypoDD relocations using cross-correlation phase arrivals.

Description: We present a quantitative procedure for constraining probabilistic seismic hazard analysis results at a given site, based on the existence of fragile geologic structures at that site. We illustrate this procedure by analyzing precarious rocks and undamaged lithophysae at Yucca Mountain, Nevada. The key metric is the probability that the feature would have survived to the present day, assuming that the hazard results are correct. If the fragile geologic structure has an extremely low probability of having survived (which would be inconsistent with the observed survival of the structure), then the calculations illustrate how much the hazard would have to be reduced to result in a nonnegligible survival probability. The calculations are able to consider structures the predicted failure probabilities of which are a function of one or more ground-motion parameters, as well as structures that either rapidly or slowly evolved to their current state over time. These calculations are the only way to validate seismic hazard curves over long periods of time.

Description: Topography-dependent eikonal equation (TDEE) formulated in a curvilinear coordinate system has been recently established and is effective for calculating first-arrival travel times in an Earth model with an irregular surface. In previous work, the Lax–Friedrichs sweeping scheme used to approximate the TDEE viscosity solutions was only first-order accurate. We present a high-order fast-sweeping scheme to solve the TDEE with the aim of achieving high-order accuracy in the travel-time calculation. The scheme takes advantage of high-order weighted essentially nonoscillatory (WENO) derivative approximations, monotone numerical Hamiltonians, and Gauss Seidel iterations with alternating-direction sweepings. It incorporates high-order approximations of the derivatives into the numerical representation of the Hamiltonian such that the resulting numerical scheme is formally high-order accurate and inherits fast convergence from the alternating sweeping strategy. Extensive numerical examples are presented to verify its efficiency, convergence, and high-order accuracy.

Description: Southwest Japan lies above an area where the Philippines Sea plate subducts beneath the Eurasian plate. The region experiences relatively high levels of crustal seismicity in addition to the interplate and intraplate seismicity associated with subduction. Crustal earthquakes are common, for example, in the Wakayama district of southwest Japan where they occur as swarmlike seismic activity. Swarm activity is common in volcanic areas but there are no Quaternary volcanic features in the Wakayama district. This report interprets crustal structure in the Wakayama district and its relationship to the swarm activity observed there. We use a new imaging method based on amplitudes of Sp -converted waves to image the spatial distribution of velocity discontinuities at high resolution. We detected four distinct velocity discontinuities at depths of 2–5, 8–13, 12–22, and 20–27 km. We interpret the 2–5 km discontinuity as the bottom of the sedimentary layer, the 12–22 km feature as the Conrad discontinuity, and the 20–27 km feature as the Moho discontinuity. The 8–13 km velocity discontinuity is detected only beneath the swarm region. The thickness of the upper crust in the swarm region was estimated to be greater than that of surrounding areas. Contrasts in the distribution of velocity discontinuities between the swarm region and surrounding areas suggest that swarm activity is generated by increased pore pressure of fluids escaping from a magmatic body ascending from the mantle.

Description: The mainshock and moderate-magnitude aftershocks of the 6 April 2009 M  6.3 L’Aquila seismic sequence, about 90 km northeast of Rome, provided the first earthquake ground-motion recordings in the urban area of Rome. Before those recordings were obtained, the assessments of the seismic hazard in Rome were based on intensity observations and theoretical considerations. The L’Aquila recordings offer an unprecedented opportunity to calibrate the city response to central Apennine earthquakes—earthquakes that have been responsible for the largest damage to Rome in historical times. Using the data recorded in Rome in April 2009, we show that (1) published theoretical predictions of a 1 s resonance in the Tiber valley are confirmed by observations showing a significant amplitude increase in response spectra at that period, (2) the empirical soil-transfer functions inferred from spectral ratios are satisfactorily fit through 1D models using the available geological, geophysical, and laboratory data, but local variability can be large for individual events, (3) response spectra for the motions recorded in Rome from the L’Aquila earthquakes are significantly amplified in the radial component at periods near 1 s, even at a firm site on volcanic rocks, and (4) short-period response spectra are smaller than expected when compared to ground-motion predictions from equations based on a global dataset, whereas the observed response spectra are higher than expected for periods near 1 s. Online Material: Velocity models used in computing theoretical site response.

Description: Induced seismicity from anthropogenic sources can be a significant nuisance to a local population and in extreme cases lead to damage to vulnerable structures. One type of induced seismicity of particular recent concern, which, in some cases, can limit development of a potentially important clean energy source, is that associated with geothermal power production. A key requirement for the accurate assessment of seismic hazard (and risk) is a ground-motion prediction equation (GMPE) that predicts the level of earthquake shaking (in terms of, for example, peak ground acceleration) of an earthquake of a certain magnitude at a particular distance. Few such models currently exist in regard to geothermal-related seismicity, and consequently the evaluation of seismic hazard in the vicinity of geothermal power plants is associated with high uncertainty. Various ground-motion datasets of induced and natural seismicity (from Basel, Geysers, Hengill, Roswinkel, Soultz, and Voerendaal) were compiled and processed, and moment magnitudes for all events were recomputed homogeneously. These data are used to show that ground motions from induced and natural earthquakes cannot be statistically distinguished. Empirical GMPEs are derived from these data; and, although they have similar characteristics to recent GMPEs for natural and mining-related seismicity, the standard deviations are higher. To account for epistemic uncertainties, stochastic models subsequently are developed based on a single corner frequency and with parameters constrained by the available data. Predicted ground motions from these models are fitted with functional forms to obtain easy-to-use GMPEs. These are associated with standard deviations derived from the empirical data to characterize aleatory variability. As an example, we demonstrate the potential use of these models using data from Campi Flegrei. Online Material: Sets of coefficients and standard deviations for various ground-motion models.

Description: A response-spectra database is compiled of hundreds of seismic records from intermediate-depth earthquakes (earthquakes whose foci are located between 45 to 300 km from the earth’s surface) with moment magnitudes of M  4.5–6.7 that occurred in the South Aegean subduction zone. The database consists of high-quality data from both acceleration-sensor and broadband velocity-sensor instruments. The database is much larger than previous databases used in the development of past empirical regressions enabling the determination of various parameters of ground-motion attenuation not previously examined. New variables accounting for the highly complex propagation of seismic waves in the Greek subduction zone are introduced based on the hypocentral depth and the location of the event, as these factors control the effects of the back-arc low-velocity/low- Q mantle wedge on the seismic-wave propagation. The derived results show a strong dependence of the recorded ground motions on both hypocentral depth and distance, which leads to the classification of the dataset into three depth-hypocentral distance categories. Ground motions from in-slab earthquakes, especially with hypocentral depths ( h )〉100 km, are amplified for along-arc stations, an expected effect of channeled waves through the high-velocity slab. The ground motions are also strongly attenuated in the back-arc region, due to the low- Q mantle wedge, which are almost independent of the recording hypocentral distance. In contrast, for shallower in-slab events (60 km〈 h 〈100 km), the corresponding differentiation of seismic motion for along-arc and back-arc stations is observed beyond a specific critical distance range. Moreover, for longer periods, both along-arc amplification and back-arc anelastic-attenuation factors strongly diminish, suggesting that the longer wavelengths of seismic waves are not affected by the complex geophysical structure, resulting in more similar ground motions for both back-arc and along-arc stations. Finally, results for interface events ( h 〈45 km) occurring along the outer Hellenic arc suggest their wave propagation is not affected by the presence of the low-velocity/low- Q S mantle wedge, but is mainly controlled by the differences of the anelastic attenuation between the Mediterranean and Aegean lithospheres.

Description: A crustal normal-faulting earthquake ( ; M w  6.7) occurred in eastern Tohoku, Japan, on 11 April 2011. K-NET and KiK-net stations recorded 82 records from within 100 km of fault rupture. These data and data from associated foreshocks and aftershocks will make a critical contribution to future improvements of ground-motion prediction for normal-faulting earthquakes. Peak ground accelerations (PGA) and peak ground velocities (PGV) are compared with four ground-motion prediction equations (GMPEs) that include the style of faulting as a predictor parameter. For distances under 100 km, and using a network average value of V S 30 , the average ratio of PGA to the selected GMPEs (the event term ) is high by factors of 2.3–3.7. Event terms for PGV are high by factors of 1.4–1.8. Adjusting PGA and PGV with customized site terms ( Kawase and Matsuo, 2004a , b ), the standard deviations of PGA and PGV residuals are reduced from 0.59 to 0.43, and from 0.53 to 0.35, respectively. The event terms decreased to relatively small factors of 1.1–1.8 for PGA and increased slightly to 1.5–2.0 for PGV. Thus, site terms are very important, but positive event terms remain. The remaining positive event terms are not explained by high stress drop, which was typical of crustal events of all mechanisms globally or in Japan. Two subparallel faults ruptured, but source inversions, which we reviewed, revealed that they ruptured sequentially, so simultaneous contributions from the two faults did not cause high motions. Although these observations may tend to suggest that ground motions in large normal-faulting events are larger than predicted by the tested models, we are not aware of any observations from this event that contradict the precarious rock evidence of Brune (2000) that ground shaking is low on the footwall near the rupture.

Description: The joint inversion of receiver function (RF) and surface-wave dispersion data is popular because it reduces the nonuniqueness of the modeled subsurface-seismic velocities. Whereas various inverse procedures have been used in joint subsurface imaging, the evaluation of uncertainties in the estimated parameter distribution is usually overlooked or considered qualitatively. We present a quantitative method for determination of uncertainty in velocity models estimated by the joint inversion of RF and surface-wave data by using the prediction of each observation sample to map the objective-function surface and create a statistical distribution of estimated model parameters. The proposed methodology is evaluated in a controlled test using synthetic data simulating a realistic shear-wave velocity model. We then apply the method to field data recorded at the POPB seismic station in the Paraná Basin, southeast Brazil. The respective range of uncertainty for modeled S -wave velocity distributions in the synthetic and field tests were 0.111–0.412 km/s (2.5%–9.2%), and 0.110–0.341 km/s (2.5%–7.9%).

Description: Because of the limited number of strong-motion records that have measured ground response at large strains, any statistical analyses of seismic site-response models subject to strong ground motions are severely limited by a small number of observations. Recent earthquakes in Japan, including the M w  9.0 Tohoku earthquake of March 2011, have substantially increased the observations of strong-motion records that can be used to compare alternative site-response models at large strains and can subsequently provide insight into the accuracy and precision of site-response models. Using the Kiban-Kyoshin network (KiK-net) downhole array data in Japan, we analyze the accuracy (bias) and variability (precision) resulting from common site-response modeling assumptions, and we identify critical parameters that significantly contribute to the uncertainty in site-response analyses. We perform linear and equivalent-linear site-response analyses at 100 KiK-net sites using 3720 ground motions ranging in amplitude from weak to strong; 204 of these records have peak ground accelerations greater than at the ground surface. We find that the maximum shear strain in the soil profile, the observed peak ground acceleration at the ground surface, and the predominant spectral period of the surface ground motion are the best predictors of where the evaluated models become inaccurate and/or imprecise. The peak shear strains beyond which linear analyses become inaccurate in predicting surface pseudospectral accelerations (PSA; presumably as a result of nonlinear soil behavior) are a function of vibration period and are between 0.01% and 0.1% for periods 〈0.5 s. Equivalent-linear analyses become inaccurate at peak strains of ~0.4% over this range of periods. We find that, for the sites and ground motions considered, site-response residuals at spectral periods 〉0.5 s do not display noticeable effects of nonlinear soil behavior. Online Material: Site-specific information and model residuals at 100 KiK-net stations.

Description: The applicability of foreign ground-motion prediction equations (GMPEs) for predicting geometric-mean pseudospectral acceleration amplitudes from active shallow crustal earthquakes in New Zealand (NZ) is examined. Four different foreign GMPEs were considered, as well as the NZ-based McVerry et al. (2006) (McV06) model. It was found that the McV06 model exhibited the lowest applicability with a database of 2437 recorded ground motions, and that the Chiou et al. (2010) (C10) modification of the Chiou and Youngs (2008b) (CY08) model was the most applicable. Discrepancies between the C10 model and the NZ database, which were empirically identified and theoretically justified, were used to modify the C10 model for: (1) small magnitude scaling; (2) scaling of short period ground motion from normal faulting events in volcanic crust; (3) scaling of ground motions on very hard rock sites; (4) anelastic attenuation in the NZ crust; and (5) consideration of the increased anelastic attenuation in the Taupo Volcanic Zone. The developed NZ-specific model therefore contains features as evident from recorded ground motions in NZ and consistent scaling for parameters not well constrained by NZ data. Comparisons with ground motions from the 4 September 2010 Darfield and 22 February 2011 Christchurch earthquakes, which occurred following completion of the NZ-specific model, illustrate that it provides an empirical prediction with sufficient accuracy and precision.

Description: Existing algorithms, including the stochastic point-source method, used to simulate synthetic ground-motion records are aimed at sampling records at a single station or records at multiple stations. The application of the algorithms may not adequately reproduce the observed coherency structure of the actual records and the intraevent spatial correlation characteristics of peak ground acceleration or spectral accelerations. To improve these, we suggest an extension to the stochastic point-source method by introducing a target spatial coherency structure and the spatially correlated uncertainties in the Fourier amplitude spectrum for each recording station. The use of the extended model to simulate the multiple-station records is illustrated, and the spatial correlation of the ground-motion measures for the simulated records are compared with the empirical spatial correlation model derived based on the 1999 Chi-Chi Taiwan earthquake.

Description: Using 3D dynamic models, we investigate the effect of fault stepovers on near-source ground motion. We use the finite-element method to model the rupture, slip, and ground motion of two parallel strike-slip faults with an unlinked overlapping stepover of variable width. We model this system as both an extensional and a compressional stepover and compare the results to those of single planar faults. We find that, overall, the presence of a stepover along the fault trace reduces the maximum ground motion when compared to the long planar fault. Whether the compressional or extensional stepover exhibits higher ground motion overall depends on the width of the separation between the faults. There is a region of reduced ground motion at the end of the first fault segment, when the faults are embedded in a homogeneous material. We also experiment with stress fields leading to supershear and subshear rupture velocities, and with different stress drops within those conditions. We find that subshear rupture produces stronger motions than supershear rupture, but supershear ruptures produce that maximum over a larger area than subshear areas, even though the overall area that experiences any shaking at all is not drastically different between the two cases. Lastly, we experiment with placing realistic materials along and around the faults, such as a sedimentary basin in an extensional stepover, a damage zone around the fault, and a soft rock layer on top of bedrock through the entire model area. These configurations alter the pattern of ground motion from the homogeneous case; the peaks in ground motion for the bimaterial cases depend on the materials in question. The results may have implications for ground-motion prediction in future earthquakes on geometrically complex faults. Online Material: MPEG-4 movies of models of dynamic rupture of fault stepovers embedded in heterogeneous material settings.

Description: The prediction of impending earthquakes undoubtedly remains one of the most pursued goals of modern seismology. Within the framework of a deterministic description of earthquake faulting, the initial state of the fault system and the choice of the governing model describing its rheological behavior play a fundamental role in the description of the earthquake recurrence. In classical models of faulting, this initial state is basically described by the initial shear-stress distribution (prior to the next earthquake event) and by the initial sliding velocity. In this paper, by assuming a rate-, state-, and temperature-dependent rheology, we investigate whether the initial thermal state of the fault can also have a significant role in earthquake dynamics. Our numerical results clearly demonstrate that the initial temperature greatly influences the cosesimic slip (and thus the earthquake magnitude), the released stress (and thus the radiated energy), and the interevent time (i.e., the earthquake recurrence). Despite the remaining issues on the concept of earthquake cyclicity, our results can contribute to the lively debate on the deterministic hazard assessment, illuminating that the temperature field also plays a fundamental role in earthquake dynamics, not only because it controls possible phase changes and the chemical environment of the fault zone, but also because it affects the response of a brittle fault and earthquake cycles.

Description: We investigate a releasing stepover between the Casa Loma and Claremont strands of the northern San Jacinto fault zone to evaluate the late Quaternary structural evolution of the fault zone, and to assess the likelihood of a rupture jumping across the stepover. Our new cone penetration test (CPT) and trench observations along the Claremont fault at Mystic Lake indicate that the main strand of the Claremont fault has jumped nearly a half kilometer westward into the San Jacinto releasing stepover during the late Quaternary. Multiple faults are inferred from the CPT data within a small sag at the northeast side of the stepover that cuts through younger stratigraphy to the west of the basin-bounding fault near Mystic Lake. Previous seismic-reflection data also suggest the presence of a young fault that cuts basin strata beneath the middle of Mystic Lake farther west of our study area. Numerous tectono-geomorphic features observed in satellite and Light Detection and Ranging Digital Elevation Model (LiDAR DEM) imagery are interpreted to delineate the location of the currently active faults, including a zone of faults that cut across the basin from the northern end of the Casa Loma fault to the Claremont fault. Seismicity observations suggest the presence of many faults within the stepover zone. Finally, new paleoseismic data from the Mystic Lake site suggest that some late Holocene earthquakes may have jumped the stepover. All of these observations suggest that the San Jacinto stepover, which has been used as the primary basis for segmenting the northern San Jacinto fault zone, is being bypassed and that the fault zone may now be capable of larger earthquakes than previously expected.

Description: We present two regional, lithospheric cross sections that illustrate eastward- and southeastward-dipping, subducted slabs to depths of 315 km beneath the surface of Colombia in northwestern South America. These cross-sectional interpretations are based on relocated earthquake hypocentral solutions, models supported on gravity and magnetic regional data, and coda-Q ( Q c ) tomography. The method of tomographic imaging based on spatial inversion of the coda wave has advantages of providing information on the lateral variations of the anelastic properties and thermal structure of the lithospheric system. Mapping of earthquake-defined Benioff zones combined with tomographic imaging reveals the presence of an ~240 km long east–west-striking slab tear, named here the Caldas tear. The proposed Caldas tear separates a zone of shallow, 20°–30°-dipping, southeastward subduction in the area of Colombia adjacent to Panama and the Caribbean Sea, which is not associated with subduction-related volcanism, from an area of steeper, 30°–40°-dipping, slab adjacent to the eastern Pacific Ocean that is associated with an active north–south chain of active arc volcanoes. We propose that the Caldas slab tear separating these two distinct subducted slabs originally formed as the southern boundary of the Panama indenter, an extinct island arc that began subducting beneath northwestern South America about 12 Ma. The area south of the Panama indenter is Miocene oceanic crust of the Nazca plate, which subducts eastward beneath northwestern South America at normal angles and melts to form a north–south-trending active volcanic arc. In addition to the formation of the Caldas tear, we propose that impedance of the thicker crustal area of the Panama arc-indenter over the past 12 Ma may have led to down-dip break-off of previously subducted oceanic crust that is marked by an extremely concentrated and active earthquake swarm of intermediate-depth earthquakes beneath east-central Colombia.

Description: Receiver-function analysis is an effective tool for investigating crustal seismological structure. Here, we present the extraction of the Moho-reflected PpPp that emerges in teleseismic P coda via a deconvolution process. Using nonlinear waveform analysis (an approach using simulated annealing technique) we estimate the source wavelet of a teleseismic P wave from records of the vertical component observed at an array of seismometers. PpPp recorded on the vertical component can be extracted by deconvolving individual vertical components by the resulting source wavelet. By employing this technique in a case study in southwestern Japan, seismic images from PpPp , as well as from Ps and PpPs , successfully image the continental Moho, the oceanic Moho, and the top surface of the Philippine Sea slab. In addition, we found that the amplitude of PpPp is useful in precisely determining crustal properties, such as vertically averaged V P / V S and the crustal thickness, by grid-search techniques. It is also important to take into account the variations of the conversion/reflection coefficients for decreasing errors of the parameters in the grid-search technique. Moreover, we demonstrate that improved seismic images of horizontal discontinuities can be obtained by using a stacking technique.

Description: We investigated the kinematic rupture along a complicated fault system during the 2008 Wenchuan earthquake. Assuming a slip distribution estimated using Interferometric Synthetic Aperture Radar (InSAR) data by Hao et al. (2009) , we tried to fit two near-fault station seismograms, one of which was located between two subparallel dipping faults. Forward numerical simulation results suggest that two subparallel dipping faults ruptured coseismically during the 2008 Wenchuan earthquake. This result provides a constraint on the dynamic fault interaction of reverse-fault earthquake, which is different from the branched strike-slip faults where the free surface does not affect the rupture branching.

Description: Low-velocity sedimentary basins introduce error in many standard receiver-function (RF) analysis techniques including common conversion point ( Dueker and Sheehan, 1997 ) and crustal thickness- V P / V S ratio ( H - ) stacking ( Zhu and Kanamori, 2000 ). We describe a simple RF analysis method for obtaining accurate crustal thickness below seismic stations located in sedimentary basins. The method extends the methods of Zhu and Kanamori (2000) . It employs an iterative two-layer depth- V P / V S stacking approach that first characterizes sediment properties (thickness and V P / V S ) allowing for the accurate interpretation of Moho conversions. Without accounting for sedimentary layers, standard-RF analysis can mischaracterize crustal thickness based on Ps -phase delay by 〉10 km beneath deep basins. We test the technique with synthetic seismograms and with data from US Array Transportable Array (TA) stations from regions with sediment thicknesses that are well determined through other means. We find sequential H - stacking for sediment properties to be a simple technique that can benefit many RF-analysis studies and can play an important role in crustal seismic studies in areas with thick or variable sediments.

Description: We describe the setup of testing regions for the China Earthquake Forecast Testing Center and provide preliminary forecast results in the scope of the Collaboratory for the Study of Earthquake Predictability (CSEP) project. We investigate the spatiotemporal variations of the completeness magnitude M c by using the frequency-magnitude distribution of the China Earthquake Networks Center (CENC) catalog. We find three periods of significantly different M c histories: (I) 1 January 1970–30 September 2001, (II) 1 October 2001–30 September 2008, and (III) 1 October 2008–31 August 2011. M c mapping provides median values , 2.2, and 1.6 for the three periods of time, respectively, showing the improvement in catalog completeness over time. We recommend using data from periods II and III to define a baseline long enough for retrospective forecast testing. Small magnitude events from period I should be used with caution due to important fluctuations in completeness. For period III, coordinates of all national and regional seismic stations are available, and we therefore apply the Bayesian magnitude of completeness (BMC) technique, mapping M c continuously by using prior information on the relationship between M c and the density of seismic stations. We define four potential testing/collection areas for CSEP-China: (A) All China, (B) North–South Seismic Belt (NSSB), (C) North and West Xinjiang Seismic Region, and (D) North China Seismic Region. In the current phase of CSEP-China, only the NSSB (region B) is considered. To demonstrate the type of earthquake predictability experiment that will be performed in the Chinese Testing Center, we present a series of retrospective forecast experiments with TripleS, a smoothed seismicity model. Online Material: The CENC earthquake catalog (1 January 1970–31 August 2011, restricted to magnitudes M ≥3.0) as well as completeness magnitude M c ( x , y ) spatial grids.

Description: We present a new method to use directly observable surface-slip measurements in seismic hazard estimates. We present measures of scaling-relation fits to slip-length data. These fits show sublinear scaling, a slowing in the rate of slip increase for the longest ruptures, so that L scaling—scaling with the length of the rupture—does not hold out to very large aspect ratio events. We find the best fitting for a constant stress-drop model, followed next by a square root of length model. The constant stress-drop model, newly introduced here, provides a geometrical explanation for a long-standing puzzle of why slip only begins to saturate at large aspect ratios. The good fit of the constant stress-drop model to the slip-length data lends further support to the observations of constant stress-drop scaling across the whole range of magnitudes of earthquakes, from small to great earthquakes. The good fit of the constant stress-drop model is also reflected by the low variability about the mean, with an average of less than a factor-of-2 variability in stress drop about the mean observed. Converting magnitude-area scaling into implied slip-length scaling, we determine qualitative consistency in the functional forms, but a quantitative difference of, on average, ~30% more slip estimated from magnitude area compared with slip length. Online Material: Tables of magnitude-length-width, magnitude-area, and surface slip-length relations.

Description: We examine the ability of teleseismic P waves to provide a timely image of the rupture history for large earthquakes using a simple, 2D finite-fault source parameterization. We analyze the broadband displacement waveforms recorded for the 2010 M w ~7 Darfield (New Zealand) and El Mayor-Cucapah (Baja California) earthquakes using a single planar fault with a fixed rake. Both of these earthquakes were observed to have complicated fault geometries following detailed source studies conducted by other investigators using various data types. Our kinematic, finite-fault analysis of the events yields rupture models that similarly identify the principal areas of large coseismic slip along the fault. The results also indicate that the amount of stabilization required to spatially smooth the slip across the fault and minimize the seismic moment is related to the amplitudes of the observed P waveforms and can be estimated from the absolute values of the elements of the coefficient matrix. This empirical relationship persists for earthquakes of different magnitudes and is consistent with the stabilization constraint obtained from the L-curve in Tikhonov regularization. We use the relation to estimate the smoothing parameters for the 2011 M w  7.1 East Turkey, 2012 M w  8.6 Northern Sumatra, and 2011 M w  9.0 Tohoku, Japan, earthquakes and invert the teleseismic P waves in a single step to recover timely, preliminary slip models that identify the principal source features observed in finite-fault solutions obtained by the U.S. Geological Survey National Earthquake Information Center (USGS/NEIC) from the analysis of body- and surface-wave data. These results indicate that smoothing constraints can be estimated a priori to derive a preliminary, first-order image of the coseismic slip using teleseismic records.

Description: Seismic data collected during explosion experiments performed as part of the TAiwan Integrated GEodynamics Research (TAIGER) project provide an excellent opportunity to obtain high-resolution images of the structure of the crust and upper mantle beneath Taiwan. The most significant feature observed at near-source stations located on the western coastal plain in Taiwan is high-energy later arrivals. These high-amplitude multiples almost completely mask the lower-amplitude signals (seismic refraction and wide-angle reflection) from the deep crust. The later arrivals are identified as free-surface-reflected multiples. The nature and generation of these high-energy, multiple diving waves are demonstrated using synthetic examples. Their generation requires the presence of a steep velocity gradient in the shallow crust. A detailed analysis of the observation data provided information on the velocity gradients in this region. An accurate layer-velocity model, including the boundary orientation and its depth, and velocity gradient, was constructed based on a 1D waveform simulation and 2D seismic raytracing modeling for travel times. The present results indicate that the thick sediment in the survey area dips shallowly to the east, has a surface P -wave velocity of , and an average velocity gradient of about 0.72/s from the surface to 3.0-km depth. The thick sediment of the 2D model shows lateral variations in velocity gradient, increasing from west to east. This velocity model may provide useful information for future data processing to reduce multiple diving waves with the aim of enhancing the deep-surface refraction/reflection signal. The velocity gradient calculated for the thick sediment of the western coastal plain may require a revision of the regional seismic velocity model developed for southwestern Taiwan, to improve the accuracy of regional hypocenter determinations, and to predict the strong ground motions produced by large earthquakes beneath this region.

Description: An attempt is made to map the spatial variation of the tectonic stress pattern in northeast India and its adjoining south Asia region using stress tensor inversion of some 516 fault-plane solutions. The Bhutan Himalaya and the Arunachal Himalaya are mapped with north–south to north-northwest–south-southeast compression. The eastern Himalaya syntaxis zone, on the other hand, shows a clockwise rotation; a north-northeast compression is dominant. To the south, in the intraplate part of the region, the Shillong plateau, Assam valley, Bengal basin (Bangladesh), and Tripura fold belt exhibit north-northwest to north-northeast compression. Orthogonal horizontal extension is dominant in southern Tibet, Bhutan, and partly in the syntaxis zone, and the same is also observed in the Shillong plateau and Assam valley area of the intraplate region. The Indo–Burma ranges and the Sagaing fault in the Myanmar region show a northeast–southwest compression; an orthogonal horizontal northwest–southeast extension is also observed in the Sagaing fault zone. A depth variation of the tectonic stress is observed below the Indo–Burma ranges; it changes from north–south to northeast–southwest in the southern part, and from northeast–southwest to north-northeast–south-southwest in the northern part in the deeper seismogenic zone. The stress inversion results of clusters of events in individual zones, though mostly conformable with the average observations, indicate a variation in the Shillong plateau due to heterogeneity and tectonic complexity.

Description: The North Anatolia Fault Zone (NAFZ) is a transform zone 1600 km in length representing the plate boundary between the westward moving Anatolian Plate and stable Eurasia. Almost the entire fault zone has failed during the last century except for the Sea of Marmara section, which is located in direct vicinity to the city of Istanbul. In this study, we investigate the crustal anisotropy along the eastern Marmara section of the NAFZ based on shear-wave splitting. We measure seismic anisotropy parameters, namely, the fast polarization direction (PD) and time delay (TD), by analyzing local seismicity recorded at selected seismographs operated throughout the eastern Sea of Marmara region. Our shear-wave splitting (SWS) observations indicate a predominant northwest–southeast-oriented PD, which is sub-parallel to both the orientation of the regional S Hmax in northwest Turkey and the local NAFZ strike along the Princes’ Islands segment. Toward the south, at the Armutlu Peninsula, we find a different PD pattern reflecting local fault strikes, S Hmax as well as strain asymmetry between different crustal blocks across the fault zone. Applying strict quality criteria enables us to identify robust, preferred fast PDs, which suggests that initially observed PD heterogeneities are sometimes caused by second-order effects in the data rather than by varying PDs. Comparing TD and hypocentral depth distribution, we find the depth extent of the anisotropy is confined to the uppermost 10-km depth of crust. We combine our SWS results with those from previous studies conducted along the San Andreas fault (SAF) and NAFZ in order to investigate the relation of angular deviations of the PDs from regional S Hmax and local fault strikes with fault-zone distance. We find that fast PDs are mainly controlled by the local fault structure in close proximity to a fault zone (5 and 10 km) while they are controlled by crustal stress at off-fault locations (5 and 10 km).

Description: Analysis of shear-wave splitting requires records of well-isolated shear waves uncontaminated by other phases. Because contamination by P -to- S or S -to- P converted waves occurs easily, we have to choose the epicentral-distance window carefully to minimize such effects. We here provide several diagrams for each of the direct s , S , ScS , and ScS2 waves, which show how systematically converted waves bias the result of a splitting analysis as a function of epicentral distance and focal depth. The diagrams were constructed using synthetic seismograms calculated up to either 2 or 0.25 Hz for a standard radially symmetric and isotropic Earth model. The data selection based on these diagrams is intended as a first step in a data selection protocol.

Description: In 1861, one of the most destructive earthquakes in the history of Argentina destroyed the city of Mendoza (currently 1 million inhabitants). The magnitude M S ~7.0 earthquake is inferred to have occurred on the 31-km-long La Cal thrust fault, which extends from Mendoza to the north, where it offsets an alluvial fan and small inset terraces along a well-preserved fault scarp. A trench excavated on a terrace that is vertically offset by ~2.5 m exposes two main stratigraphic units separated by an erosional unconformity. The coarse-grained upper unit is deformed by three east-vergent folds ( F 1 – F 3 ). Retrodeformation of these folds yields total displacements of ~2.0 m, ~2.4 m, and ~0.5 m on the underlying fault splays, respectively. The displacement of ~2.0 m recorded by fold F 1 is interpreted as the result of the fault rupture that caused the 1861 earthquake. F 2 and F 3 were presumably generated during the penultimate event with an inferred magnitude of M w ~7.0, although formation during two distinct ruptures cannot be excluded. Finite-element modeling shows that coseismic folding above the tip of a blind thrust fault is a physically plausible mechanism to generate these folds. A published luminescence age of 770±76 years, which is interpreted to date the formation of the deformed terrace, indicates that the two (or possibly three) scarp-forming events occurred during the last ~800 years. The fine-grained sediments below the erosional unconformity—that contain evidence for at least one older earthquake—are dated at ~12 kyr. Our results indicate that elastic strain energy, which is accumulating at the front of the Precordillera today as shown by Global Positioning System (GPS) data, was repeatedly released during earthquakes on the La Cal fault in the past. Hence, the La Cal thrust fault poses a serious threat to the city of Mendoza.

Description: We show how the maximum magnitude within a predefined future time horizon may be estimated from an earthquake catalog within the context of Gutenberg–Richter statistics. The aim is to carry out a rigorous uncertainty assessment, and calculate precise confidence intervals based on an imposed level of confidence α . In detail, we present a model for the estimation of the maximum magnitude to occur in a time interval T f in the future, given a complete earthquake catalog for a time period T in the past and, if available, paleoseismic events. For this goal, we solely assume that earthquakes follow a stationary Poisson process in time with unknown productivity and obey the Gutenberg–Richter law in magnitude domain with unknown b -value. The random variables and b are estimated by means of Bayes theorem with noninformative prior distributions. Results based on synthetic catalogs and on retrospective calculations of historic catalogs from the highly active area of Japan and the low-seismicity, but high-risk region lower Rhine embayment (LRE) in Germany indicate that the estimated magnitudes are close to the true values. Finally, we discuss whether the techniques can be extended to meet the safety requirements for critical facilities such as nuclear power plants. For this aim, the maximum magnitude for all times has to be considered. In agreement with earlier work, we find that this parameter is not a useful quantity from the viewpoint of statistical inference.

Description: The countries of Jamaica, Haiti, and the Dominican Republic all straddle the Enriquillo–Plantain Garden fault zone (EPGFZ), a major left-lateral, strike-slip fault system bounding the Caribbean and North American plates. Past large earthquakes that destroyed the capital cities of Kingston, Jamaica (1692, 1907), and Port-au-Prince, Haiti (1751, 1770), as well as the 2010 Haiti earthquake that killed more than 50,000 people, have heightened awareness of seismic hazards in the northern Caribbean. We present here new geomorphic and paleoseismic information bearing on the location and relative activity of the EPGFZ, which marks the plate boundary in Jamaica. Documentation of a river bank exposure and several trenches indicate that this fault is active and has the potential to cause major destructive earthquakes in Jamaica. The results suggest that the fault has not ruptured the surface in at least 500 yr and possibly as long as 28 ka. The long period of quiescence and subdued geomorphic expression of the EPGFZ indicates that it may only accommodate part of the ~7–9 mm/yr plate deformation rate measured geodetically and that slip may be partitioned on other undocumented faults. Large uncertainties related to the neotectonic framework of Jamaica remain and more detailed fault characterization studies are necessary to accurately assess seismic hazards.

Description: A Roman mausoleum located in the ancient city of Pinara, southwest Turkey, shows traces of strong dynamic forces. Considering the seismotectonic potential of the area, earthquake ground motions are a potential cause of damage. On the other hand, the mausoleum is located at the foot of an almost 100-m-high steep cliff imposing rockfall hazard to the building. We constructed a 3D model of the mausoleum based on 90 million points from nine laser scans. From this model the shape and size of the construction was measured and the displacements of all visible block vertices have been derived. Based on the 3D model and examples of similar structures a fully reconstructed virtual discrete-element model of the mausoleum with 180 individual blocks was constructed. This model was exposed to earthquake ground motions and the impact of falling rocks. The impact velocity of the latter was estimated with a site-specific rockfall model. The earthquake ground motion was estimated from local earthquake scenarios and quantified with 3D synthetic strong-motion seismograms. In addition, analytic ground-motion signals were used to study the general dynamic behavior of the mausoleum and the vulnerability of its columns. Comparison of the in situ measured block displacements and the damage pattern with the results of the rockfall and earthquake models clearly favor coseismic displacement as the cause of the damage. A local earthquake with moment magnitude 6.3 is sufficient to produce the observed damage.

Description: The paper reports on the use of surface-wave testing for the construction of a three-dimensional (3D) shear-wave velocity model of an alluvial basin. The town of Tarcento (Italy) is located in a region with a high level of seismic hazard and was strongly affected by the two Friuli earthquakes in 1976. The seismic surveys were performed with surface-wave multistation methods using a combination of active-source and passive-source experimental setup. Experimental data were collected at 16 sites, and inversion of the data is based on an innovative procedure for spatially constrained inversion with a single objective function in which a priori information is included. The method provides an improvement in the robustness of the solution, mitigating solution nonuniqueness. Available borehole logs at different locations are integrated into the data set in terms of a priori bedrock information. Three independent cross-hole tests are used for a posteriori comparison of the inverted one-dimensional (1D) profiles. Three-dimensional interpolation of the obtained profiles leads to a shear-wave velocity model that is internally consistent and complies with a priori information, cross-hole results, and suitable boundary profiles. The model is intended for numerical simulations of the seismic response of the basin. Online Material: Figure showing the a priori bedrock surface.

Description: While site response phenomena are well recognized globally, the influence of regolith properties on ground motion has not previously been investigated for much of Australia. In an effort to characterize the regolith in terms of its ability to modify earthquake ground shaking, this validation study assesses the national site classification map of Australia, which has been developed for application in first-order earthquake hazard and risk assessment. In the absence of regolith thickness and fundamental period data, site classes are assigned based on a method developed in California that uses the relationship between geological material and the shear-wave velocity of the upper 30 m ( V S 30 ). The classification scheme is then adjusted to suit the Australian geological environment, including a correction for the presence of weathered in situ regolith commonly encountered in this stable tectonic setting. The results are validated using geophysical and geotechnical data from a variety of Quaternary sedimentary environments in the Newcastle, Sydney, and Perth urban areas, and from bedrock-dominated environments at a range of sites across Australia. The results of these analyses demonstrate the utility, but also highlight the limitations, of applying a depth-limited shear-wave velocity method in site classification for seismic hazard assessment.

Description: The earthquake motion generated by the multiple scattering due to the complexity of the underneath soil structure can be referred to as a diffuse wave field. Under the assumption of the well-diffused wave field it is accepted that the average autocorrelation of a single receiver is proportional to the imaginary part of the Green’s function when both source and receiver are located at the same point. In this study we focus on sites where the site effect can be described using a 1D model. Previous studies show that the imaginary part of the Green’s function at the free surface is proportional to the square of the absolute value of the corresponding transfer function for a plane, vertically incident wave with unit amplitude. It is then possible to carry out an inversion of the 1D velocity structure using the relationship between the horizontal-to-vertical (H/V) spectral ratio and the ratio of horizontal and vertical transfer functions. We verify that the average H/V spectral ratio computed with a sufficiently large number of earthquake data depends only on the underneath geological structure and not on the set of data used to compute it. We then carry out inversions of the velocity structures for 10 sites of the K-NET and KiK-net networks in the Tohoku area, Japan, following the proposed theory for earthquake H/V spectral ratios. We verify that there is a good match between the observed H/V spectral ratios and the theoretical ones corresponding to the proposed velocity structures for the 10 target sites studied in the present work. Online Material: Figures showing variations of H/V spectral ratios and results of the inversions and tables of inversion parameters.

Description: The conditional spectrum (CS) is a target spectrum (with conditional mean and conditional standard deviation) that links seismic hazard information with ground-motion selection for nonlinear dynamic analysis. Probabilistic seismic hazard analysis (PSHA) estimates the ground-motion hazard by incorporating the aleatory uncertainties in all earthquake scenarios and resulting ground motions, as well as the epistemic uncertainties in ground-motion prediction models (GMPMs) and seismic source models. Typical CS calculations to date are produced for a single earthquake scenario using a single GMPM, but more precise use requires consideration of at least multiple causal earthquakes and multiple GMPMs that are often considered in a PSHA computation. This paper presents the mathematics underlying these more precise CS calculations. Despite requiring more effort to compute than approximate calculations using a single causal earthquake and GMPM, the proposed approach produces an exact output that has a theoretical basis. To demonstrate the results of this approach and compare the exact and approximate calculations, several example calculations are performed for real sites in the western United States. The results also provide some insights regarding the circumstances under which approximate results are likely to closely match more exact results. To facilitate these more precise calculations for real applications, the exact CS calculations can now be performed for real sites in the United States using new deaggregation features in the U.S. Geological Survey hazard mapping tools. Details regarding this implementation are discussed in this paper.

Description: We introduce a procedure for selecting and ranking of ground-motion prediction equations (GMPEs) that can be useful for regional or site-specific probabilistic seismic hazard assessment (PSHA). The methodology is called Euclidean distance-based ranking (EDR) as it modifies the Euclidean distance ( DE ) concept for ranking of GMPEs under a given set of observed data. DE is similar to the residual analysis concept; its modified form, as discussed in this paper, can efficiently serve for ranking the candidate GMPEs. The proposed procedure separately considers ground-motion uncertainty (i.e., aleatory variability addressed by the standard deviation) and the bias between the observed data and median estimations of candidate GMPEs (i.e., model bias). Indices computed from the consideration of aleatory variability and model bias or their combination can rank GMPEs to design GMPE logic trees that can serve for site-specific or regional PSHA studies. We discussed these features through a case study and ranked a suite of GMPEs under a specific ground-motion database. The case study indicated that separate consideration of ground-motion uncertainty (aleatory variability) and model bias or their combination can change the ranking of GMPEs, which also showed that the ground-motion models having simpler functional forms generally rank at the top of the list. We believe that the proposed method can be a useful tool to improve the decision-making process while identifying the most proper GMPEs according to the specific objectives of PSHA. Online Material: MATLAB script and sample input file for EDR index calculation.

Description: Recent upward revision of the 1872 Owens Valley earthquake from M w  7.4–7.5 to 7.7–7.9 implies either additional unrecognized rupture length or anomalously strong ground motions associated with this event. We investigate the first possibility through paleoseismic trenching south of the mapped surface rupture in the Haiwee area, where historical accounts suggest significant surface deformation following the earthquake. Trenching focused on a prominent north-striking scarp, herein termed the Sage Flat fault, expressed in Pleistocene alluvial fans east of Haiwee Reservoir. Surficial mapping and ground-based Light Detection and Ranging (lidar) surveying suggest that this fault accommodates east-down normal motion, and possibly a comparable amount of dextral slip. Trenching and luminescence dating brackets the timing of the most recent surface-rupturing earthquake between ~25.7 and 30.1 ka, and provides evidence for an earlier event predating this time. In combination with scarp profiling, these dates also suggest a maximum rate of normal, dip-slip fault motion up to ~0.1 mm/yr over this period. Although we discovered no evidence for recent surface rupture on the Sage Flat fault, a series of subvertical fractures and fissures cut across young trench stratigraphy, consistent with secondary deformation associated with seismic shaking. As such, we suggest that possible ground disturbance in the Haiwee area during the 1872 event primarily reflected ground shaking or liquefaction-related deformation rather than triggered slip. In addition, we infer a structural and kinematic connection between the Owens Valley fault and oblique-dextral faults north of Lower Cactus Flat in the northwestern Coso Range, rather than a west-step into northern or western Rose Valley. Consideration of these structures in the total extent of the Owens Valley fault suggests a length of 140 km, of which at least 113 km ruptured during the 1872 event. Online Material: Procedural details and expanded results from the OSL sample analyses, as well as high-resolution paleoseismic trench logs.

Description: The Lower Rhine Graben (LRG) straddling the border zone of Belgium, the Netherlands, and Germany, is an active tectonic structure in continental northwest Europe. It is characterized by northwest–southeast oriented normal faults, and moderate but rather continuous seismic activity. Many faults have been mapped in the LRG, but so far a model of fault hierarchy or fault segmentation has been lacking. In the frame of a European database of seismogenic sources, we have devised a seismic-source model for the LRG consisting of so-called composite seismic sources. Each composite seismic source may encompass one or more segments, but it is unlikely that a segment would extend across more than one source. We distinguish 15 seismic sources based on major stepovers, bifurcations, gaps, and important changes in strike, dip direction, or slip rate. The sources are partitioned into one or more informal fault sections, each with an associated surface trace. For each source, we describe the limits and the composing fault sections, and present the geological arguments for their existence. We have compiled all relevant data concerning the seismic-source parameters required for the database, putting lower and upper bounds on strike, dip, rake, slip rate, and depth, and an upper bound on earthquake magnitude. This source model should provide a new basis for modeling seismic hazard, as well as for guiding further paleoseismic studies in the LRG. Online Material: Detailed maps of the composite sources in the Lower Rhine Graben, 3D views of the fault model, and a table with parameters of earthquake focal mechanisms and detailed information sheets for each composite seismic source.

Description: A backprojection method is applied to the 27 February 2010 M w  8.8 and 25 March 2012 M w  7.1 Maule, Chile, earthquakes using high-frequency (0.8–2 Hz) USArray data. During the 2010 event, highest energy release occurred north of the epicenter, with two subevents comprising this rupture. The gap between these subevents was about 100 km and 15 s, suggesting that P waves from the first subevent dynamically triggered the second subevent. This triggering can be explained as a consequence of stopping phases generated at the terminus of subevent 1, as the rupture encounters a region of low interseismic coupling. This argument is supported by the occurrence of the 2012 M w  7.1 event, which is the largest interface earthquake since the 2010 mainshock and ruptured an area that completely filled the gap left from the mainshock. Seismic gaps, regions between the slip areas of past giant earthquakes, are known to have a higher potential for generating future large events. The results of this study show that a coseismic gap behaves similarly, and detailed imaging of rupture propagation can be used to identify areas that may produce large earthquakes. A comparable coseismic gap to the 2010 Chile gap is identified for the 2011 M w  9.0 Tohoku, Japan, earthquake that may be the site of a large event in the near future. Online Material: Figures showing point source synthetic tests for the back projection method, station location, and distribution of energy release.

Description: Knowledge of the acceleration spectral shape is crucial to various applications in engineering seismology. Spectral amplitude decays rapidly at high frequencies. Anderson and Hough (1984) introduced the empirical factor to model this attenuation. This is the first time is studied in a vertical array consisting of more than two stations. We use 180 earthquakes recorded at a downhole array with five stations in soils and rock to investigate the effect of soil conditions on . Given that computation processes vary across literature when following the classic Anderson–Hough method, we investigate its variability with the different assumptions that can be made when applying the method. The estimates of 0 range between 0.017 and 0.031 s at the surface and between 0.004 and 0.024 s at rock. This variability due to the assumptions made is larger than the error of each estimate and larger than the average difference in values between sediment and rock. For this data set, part of it can be attributed to the type of distance used. Given this variability, 0 values across literature may not always be comparable; this may bias the results of applications using 0 as an input parameter, such as ground-motion prediction equations. We suggest ways to render the process more homogeneous. We also find that at rock level is not well approximated by surface records from which we deconvolved the geotechnical transfer function. Finally, we compute on the vertical component and find a dependence of the vertical-to-horizontal ratio on site conditions. Online Material: Table of regression parameters and figure showing the regressed lines.

Description: This paper uses microtremor-array measurements to obtain an overall view of S -wave velocity structure in the Chiayi area, Taiwan. The Rayleigh-wave dispersion curves are calculated using the frequency-wavenumber ( ) spectrum method and then the S -wave velocity structure of the area is estimated by surface-wave inversion. According to the inversion results, the S -wave velocities decrease from east to west. If the S -wave velocity of the bedrock is assumed to be 1500 m/s, the depths of the alluvium are between 560 and 1400 m gradually increasing from east to west. In order to understand the variations of the shallow S -wave velocity in the area, we sketch 2D and 3D maps using the imaging techniques based on interpolation algorithms. From the 3D results, the thickness of the sediments having an S -wave velocity in the range 270–1500 m/s increases from east to west; whereas the thickness of the layers having an S -wave velocity in the range 1500–2370 m/s decreases from east to west. The results are also in good agreement with the geological and geophysical information of the Chiayi area. Therefore, microtremor-array measurement provides a good alternate to estimate shallow S -wave velocity structure. Online Material: Figures showing observed and calculated phase velocities, f - k spectra, dispersion curves, inverted velocity models, sensitivity kernels, and V S contour maps and electric resistivity maps.

Description: Spatial correlations of ground-motion intensity measures (IMs) are essential for seismic analysis of spatially distributed systems. In this paper, geostatistical analysis is conducted to calculate the spatial correlations for cumulative absolute velocity (CAV), Arias intensity (Ia), and spectral accelerations (SA) using a total number of more than 1500 earthquake records from nine recent earthquakes occurred in Taiwan, California, and Japan. The results indicate that the spatial correlations for these IMs are closely related to the regional site conditions, and they can be predicted based on the spatial correlations of shear-wave velocity in the top 30 m ( V S 30 ). In general, an IM recorded from a relatively homogeneous regional site condition tends to have a larger spatial correlation range than that from a heterogeneous site condition. Due to their intrinsic similarity to represent the integration of acceleration time histories, CAV and Ia have similar spatial correlation coefficients. Besides, the range of spatial correlation of SA generally increases as the spectral period increases. Simple predictive equations are proposed in this study to quantify the spatial correlations of CAV, Ia, and SA based on regional site conditions. Methods for data correction are also proposed to eliminate artificial correlations due to biased distance scaling and V S 30 estimation in the database. Finally, Monte Carlo method is used to generate spatially distributed IMs. The results demonstrate that the annual frequency of exceedance curves for spatially distributed IMs differ significantly if different ranges of spatial correlations are used.

Description: We observe enhanced high-frequency radiation of P waves from aftershocks of the 4 April 2010 ( M w  7.2), El Mayor–Cucapah, Baja California, earthquake that may reflect isotropic radiation generated by rock damage in the source regions. To eliminate path, radiation pattern, and site effects we use spectral ratios of four pairs of collocated events with similar size and focal mechanism that occurred within short time intervals (less than 24 hrs) and were recorded at the same stations. The P / P and the S / S spectral ratios calculated for the selected pairs of events show that events with similar size may have differences of high-frequency radiation up to a factor of 4 at 10 Hz and up to a factor of 10 at 4 Hz for P and S waves, respectively. To evaluate the differences between P - and S -wave energy radiated at high frequencies, we calculate the ( P / P )/( S / S ) ratio of the ratios at high frequencies ( f 〉1.5 Hz) in a band for which the signal-to-noise ratio is adequate. Since the pairs of used events have approximately the same size, the ratio of ratios is expected to be near unity. We observed high ( P / P )/( S / S ) spectral ratios at high frequencies ( f 〉6 Hz), up to a factor of 9, which may reflect isotropic radiation associated with rock damage. To find additional possible signatures of rock damage, we evaluate changes of coda Q using the same data. The results show small change of Q for a doublet located on the Laguna Salada fault. However, for the doublets located south of the Sierras El Mayor–Cucapah, where there was no surface rupture before the sequence, changes of Q at 5 Hz by a factor of about 3 indicate significant temporal variations of rock properties along the source–receiver path.

Description: Resolving earthquake parameters, especially depth, is difficult for events occurring within basins because of issues involved with separating source properties from propagational path effects. Here, we demonstrate some advantages of using a combination of teleseismic and regional waveform data to improve resolution following a bootstrapping approach. Local SS - S differential arrivals from a foreshock are used to determine a local layered model which can then be used to model teleseismic depth phases: pP , sP , and sS . Using the cut-and-paste (CAP) method for which all strike ( ), dip ( ), rake ( ), and depth variations are sampled for several crustal models. We find that regional data prove the most reliable at fixing the strike, whereas the depth is better constrained by teleseismic data. Weighted solutions indicate a nearly pure strike-slip mechanism ( =59°±1°) with a centroid depth of about 4.0 km and an M w of 5.4 for the mainshock of the 2012 Brawley earthquake. Online Material: Figures showing examples of waveform fits, comparison of synthetic teleseismic waveforms using different grid sizes in the FD calculation, effect of soft sediment on teleseismic Green's functions, and sensitivity of regional and teleseismic data on the focal mechanisms.

Description: We estimated frequency-dependent attenuation of coda waves ([IMG]/medium/109eq1.gif" ALT="Formula "〉) and body waves ([IMG]/medium/109eq2.gif" ALT="Formula "〉 and [IMG]/medium/109eq3.gif" ALT="Formula "〉) in 1.5-24 Hz by applying the single isotropic scattering theory and the extended coda-normalization method, respectively, in the crust beneath the Andaman Sea. We used 43 aftershocks of the 13 September 2002 earthquake (Mw 6.5) in the Andaman Sea recorded by three stations installed in the Andaman Islands. The coda Q factors calculated from the amplitude decay rate of the S-wave coda show a dependence on frequency and lapse time. We found that with the increase in lapse time window from 10 to 40 s, Q0 (QC at 1 Hz) increases from 55 to 153, while the frequency-dependent coefficient n decreases from 1.1 to 0.94. The average frequency-dependent relations of [IMG]/medium/109eq4.gif" ALT="Formula "〉 vary from 0.02f-1.1 to 0.01f-0.94 with an increase in lapse time window from 10 s to 40 s, respectively. The values of [IMG]/medium/109eq5.gif" ALT="Formula "〉 and [IMG]/medium/109eq6.gif" ALT="Formula "〉 corresponding to spectral amplitude decays show strong frequency dependence and are expressed as 0.02f-1.01 and 0.01f-1.0, respectively. Our results are consistent with those of other seismically active regions. The ratio [IMG]/medium/109eq7.gif" ALT="Formula "〉 is found to be larger than unity for the whole frequency range. We separated intrinsic absorption ([IMG]/medium/109eq8.gif" ALT="Formula "〉) and scattering attenuation ([IMG]/medium/109eq9.gif" ALT="Formula "〉) using the independent estimates of [IMG]/medium/109eq10.gif" ALT="Formula "〉 and [IMG]/medium/109eq11.gif" ALT="Formula "〉. The results show that [IMG]/medium/109eq12.gif" ALT="Formula "〉 is close to [IMG]/medium/109eq13.gif" ALT="Formula "〉 and both of them are larger than [IMG]/medium/109eq14.gif" ALT="Formula "〉, suggesting that coda decay is predominantly caused by intrinsic attenuation.

Description: The earthquake ground-motion prediction equations developed for the Next Generation Attenuation of Ground Motions (NGA-West) project in 2008 have established a new baseline for the estimation of ground-motion parameters, such as peak ground acceleration, peak ground velocity, and spectral acceleration, for shallow crustal earthquakes in active tectonic regions. We perform statistical goodness-of-fit analyses to quantitatively compare the predictive capabilities of the NGA models and their predecessors, using several testing subsets of the master database used in model development. In addition, we perform a blind comparison test using 1060 ground-motion records from seven recent earthquakes recorded in California: the 2003 M 6.5 San Simeon event, 2004 M 6.0 Parkfield event, 2005 M 5.2 Anza event, 2007 M 5.4 Alum Rock event, 2008 M 5.4 Chino Hills event, 2010 M 7.2 Baja event, and 2010 M 5.7 Ocotillo event. We assess how modeling decisions regarding the regression dataset, functional forms, input parameters, and model complexity influence the models' predictive capabilities. By comparing the performance of each model, we discuss various ground-motion modeling strategies and offer recommendations for model development. We find that increased model complexity does not necessarily lead to increased prediction accuracy, that the inclusion of aftershocks in regression datasets may result in decreased predictive capabilities for mainshocks, and that the use of measured site characteristics leads to greatly improved ground-motion predictions. A model validation framework is introduced to assess the prediction accuracy of ground-motion prediction equations and to aid in their future development.

Description: Changes to building codes in the last decade, lowering the probability at which design ground motions for geotechnical applications are defined, have led to an urgent need for a probabilistic approach/tool for liquefaction potential assessment. We propose a consistent approach for probabilistic liquefaction hazard analysis (PLHA) that is based on probabilistic seismic hazard analysis and incorporates a reliability-based liquefaction potential evaluation method based on shear-wave velocity data. The method directly takes the joint probability distribution of peak ground acceleration and moment magnitude into account. We demonstrate the method for four Canadian cities, employing our interim updated seismic hazard models for eastern and western Canada. Using the developed method and representative site profiles, PLHA is implemented for four major cities across Canada with the aim of investigating the impact of regional seismic characteristics on liquefaction hazard assessment. Sensitivity analysis indicates that different magnitude ranges of dominant contributing seismic events have significant impact on the extent of liquefaction hazard. More specifically, for a given seismic excitation level, the relatively high hazard contributions from small-to-moderate earthquakes in eastern Canada leads to less significant liquefaction potential, in comparison with similar sites in western Canada.