ALBERT

Description: Here, the generalized inversion of S -wave amplitude spectra is employed for deriving the site response and S -wave attenuation (quality factor) in the northwest region of Iran. A total of 279 strong-motion accelerograms recorded at distances below 200 km from 41 earthquakes with moment magnitudes ranging from M w  3.8 to 6.5 are used to determine the region-specific attenuation model. The site responses have been determined for all 54 stations individually. The bulk of strong-motion data (i.e., 184 records) comes from the 2012 Ahar–Varzaghan dual earthquakes in northwest Iran and their aftershocks. Also, the modified finite-fault method, which is able to model nonuniform stress distribution on the fault plane, is employed to investigate the coseismic stress parameter for the first and second Ahar–Varzaghan dual earthquakes by minimizing the difference between the synthesized and observed pseudospectral accelerations for 5% damping. Results denote a concentration of stress drops on the northwestern part of the first event’s fault and on the central and eastern part of the second fault. Stochastic simulations, using the calibrated stress distribution have been performed on a regular grid covering the study area for both rock- and soil-site conditions (in total, 651 points). The results show that the maximum of peak ground accelerations (PGAs) during the Ahar–Varzaghan dual earthquakes for the rock-site condition reached 557 cm/s/s, and the largest peak ground velocities (PGVs) were estimated around 76 cm/s. In general, comparisons between simulated data and empirical ground-motion prediction equations (GMPEs) show that the stochastic predictions (PGAs and PGVs) are higher than those predicted by the empirical GMPEs for distances less than 30 km and are smaller for distances more than 30 km. The simulated data are also consistent with the modified Mercalli intensity observations and show reasonable agreement. This can be considered as another validation of the method.

Description: In a low-seismicity context, the use of numerical simulations becomes essential due to the lack of representative earthquakes for empirical approaches. The goals of the EUROSEISTEST Verification and Validation Project (E2VP) are to provide (1) a quantitative analysis of accuracy of the current, most advanced numerical methods applied to realistic 3D models of sedimentary basins (verification) and (2) a quantitative comparison of the recorded ground motions with their numerical predictions (validation). The target is the EUROSEISTEST site located within the Mygdonian basin, Greece. The site is instrumented with surface and borehole accelerometers, and a 3D model of the medium is available. The simulations are performed up to 4 Hz, beyond the 0.7 Hz fundamental frequency, thus covering a frequency range at which ground motion undergoes significant amplification. The discrete representation of material heterogeneities, the attenuation model, the approximation of the free surface, and nonreflecting boundaries are identified as the main sources of differences among the numerical predictions. The predictions well reproduce some, but not all, features of the actual site effect. The differences between real and predicted ground motions have multiple origins: the accuracy of source parameters (location, hypocentral depth, and focal mechanism), the uncertainties in the description of the geological medium (damping, internal sediment layering structure, and shape of the sediment-basement interface). Overall, the agreement reached among synthetics up to 4 Hz despite the complexity of the basin model, with code-to-code differences much smaller than predictions-to-observations differences, makes it possible to include the numerical simulations in site-specific analysis in the 3D linear case and low-to-intermediate frequency range.

Description: Response spectra for California earthquakes of 3.0≤ M 〈7.5 are well described by a simple stochastic ground-motion model using an equivalent point-source concept. We determine the best-fit stress parameter of each California earthquake in the Next Generation Attenuation-West 2 database based on matching simulated to observed response spectral shapes over a wide frequency range, and we derive an expression for the mean stress as a function of magnitude and focal depth. A calibration factor is calculated for each event; this constant is the required amplitude adjustment in order that the simulations match the observed response spectral amplitudes with zero bias. The best-fit simulation model suggests that the attenuation in California can be modeled as R –1.3 at distances 〈50 km and R –0.5 at further distances; this does a better job at matching attenuation trends than the traditional model 1/ R model at distances 〈50 km, particularly for M 〈5.5 events. The model requires an overall multiplicative calibration factor of C sim =3.16 in order for the simulations to match the observed response spectral amplitudes, for all magnitudes and distances. The calibration constant could be attributed to simplifications inherent in the modeling of source, attenuation, and site processes, and the lack of consideration of multiple phases in stochastic simulations. We conclude that the equivalent point-source simulation method with the proposed modeling parameters can predict average ground motions in California, generally within a ±25% error band, for magnitudes up to M  7.5, distances 〈400 km, and frequencies 〉0.2 Hz. We finish the paper by providing a recipe for developing a simulation-based generic ground-motion prediction equation that can be adjusted for source and attenuation attributes in different regions by simple modifications to its key source and attenuation modeling parameters.

Description: We analyzed the regional dependence of ground motion to intensity conversion equations and derived a new global relationship to improve ground motion and intensity estimates for earthquake hazard applications, including those related to the ShakeMap system. For this purpose, we merged several databases collected by other authors in different geographical regions to highlight any systematic regional effects in the relationship between macroseismic intensities and both peak ground velocity and peak ground acceleration. Our database contains macroseismic intensities derived from expert assignments or from the "Did You Feel It?" database, paired with peak ground motions (PGM) from seismic stations. We constrain our intensity–ground-motion pairs to those with a maximum 2 km separation. For each region, we derived invertible relationships between intensities and ground motion using an orthogonal regression. We also derived a global relationship to quantify the regional differences. We investigated the dependence of intensity on predictor variables such as PGM, magnitude, and hypocentral distance. Our analyses indicate that PGM is the most robust predictor variable of intensity. Within one standard deviation, our regional and global results are in agreement with the relations of Worden et al. (2012) for California, Faenza and Michelini (2010) for Italy, Tselentis and Danciu (2008) for Greece, and Atkinson and Kaka (2007) for central–eastern United States. The earthquakes in the study ranged in magnitude from 2.5 to 7.3, and the distances ranged from less than a kilometer to about 200 km from the epicenter. Online Material: Table summarizing published relationships and figures showing the relationship between peak ground acceleration and intensity.

Description: The peak ground acceleration (PGA) and peak ground velocity (PGV) from 5058 ruptures of a foam rubber stick-slip model are not distributed according to a lognormal probability distribution function. PGA and PGV values are decomposed using the method of Anderson and Uchiyama (2011) . The statistically significant deviations from the lognormal distribution occur near the peak of the distribution. In some cases, high-amplitude tails differ by a much greater ratio, but the statistical significance of this effect is low. This result is true of both raw data and data adjusted for site and magnitude. Event terms are also not lognormal but can be modeled as a sum of three or four lognormal subdistributions, which possibly represent different preferred rupture initiation points rather than a uniform distribution of initiation points. The event term subdistributions with highest median values have small standard deviations, so if shapes of this nature were used in ground-motion prediction equations (GMPEs) during a probabilistic seismic-hazard analysis, the effect of the long tail of the lognormal distribution in controlling the hazard would be weakened considerably. Static stress drop was recorded for each event, and event terms for PGA and PGV are well correlated with static stress drop. Unlike Next Generation Attenuation-West 2 GMPEs, residual variances for the foam model are dominated by variability in the source slip function, rather than the path and site effects. This difference in the variance budget results from the way in which the source and site residuals are defined in this study; the source uncertainty includes variation in the rupture size (magnitude) and location, along with deviations in distance and path. We do not know if these results apply to earthquakes, but we do think tests of repeating stick-slip events in a physical system are useful to expand the set of credible hypotheses regarding possible behavior modes of earthquake faults.

Description: The M w  5.8 Awajishima earthquake occurred on 13 April 2013 in southwest Awaji Island, ~25 km southwest of the epicenter of the 1996 M w  6.8 Kobe earthquake, southwest Japan. Analyses of aerial photographs and 3D perspective images, field investigations, and structural analysis of fault rocks reveal that: (1) a previously undocumented fault, here called the Yamada fault, strikes northwest–southeast and dips southwest at 86° along a topographic lineament at the geological boundary between Mesozoic granitic rocks and the late Pliocene–Quaternary Osaka Group composed of interbedded sandstone and mudstone; (2) the main shear zone of the Yamada fault consists of a fault core with a 〈10 cm wide zone of fault gouge (generally 1–5 cm), a fault breccia zone of 〈100 cm wide, and a damage zone of 10–50 m wide, composed of cataclastic rocks and fractures; (3) foliations characterized by S-C fabrics that have developed in the shear zone indicate a dominantly thrust fault sense, consistent with that revealed by the focal mechanism; and (4) coseismic surface ruptures occurred locally along the main trace of the Yamada fault, consisting of numerous short fissures ranging in length from centimeters to several meters and concentrated in a zone 〈5 m wide. Our findings show that the newly identified Yamada fault is an active fault and that it is probably the fault on which the 2013 M w  5.8 Awajishima earthquake occurred. Therefore, it is necessary to construct a fault model to better understand the deformation characteristics of the seismogenic source fault and for reassessing the seismic hazards on the densely populated Awaji Island of southwest Japan.

Description: We perform numerical simulations of dynamic rupture processes along the North Anatolian fault in the Sea of Marmara, which poses a high risk to the nearby city of Istanbul. Several fault geometry models, nucleation points, and initial stress states are tested. The likelihood of each earthquake scenario is evaluated, and a probabilistic assessment of the ground-motion estimation is proposed. The simulation results suggest that the fault geometrical configuration is not favorable for producing an earthquake of magnitude 6–7, as no scenario is found. On the contrary, the probability of occurrence of an earthquake of magnitude greater than 7 is high. Most of these large events are characterized by epicenters located in the central or eastern parts of the Sea of Marmara. However, the possibility of a western-initiated rupture propagating eastward, the worst scenario for the Istanbul region, cannot be ruled out. Many simulations led to supershear ruptures, as observed for the nearby 1999 Izmit earthquake, and this significantly influences ground-motion prediction in the region.

Description: In this study, we analyze acoustic emission (AE) data recorded at the Morsleben salt mine, Germany, to assess the catalog completeness, which plays an important role in any seismicity analysis. We introduce the new concept of a magnitude completeness interval consisting of a maximum magnitude of completeness ( M c(max) ) in addition to the well-known minimum magnitude of completeness. This is required to describe the completeness of the catalog, both for the smallest events (for which the detection performance may be low) and for the largest ones (which may be missed because of sensors saturation). We suggest a method to compute the maximum magnitude of completeness and calculate it for a spatial grid based on (1) the prior estimation of saturation magnitude at each sensor, (2) the correction of the detection probability function at each sensor, including a drop in the detection performance when it saturates, and (3) the combination of detection probabilities of all sensors to obtain the network detection performance. The method is tested using about 130,000 AE events recorded in a period of five weeks, with sources confined within a small depth interval, and an example of the spatial distribution of M c(max) is derived. The comparison between the spatial distribution of M c(max) and of the maximum possible magnitude ( M max ), which is here derived using a recently introduced Bayesian approach, indicates that M max exceeds M c(max) in some parts of the mine. This suggests that some large and important events may be missed in the catalog, which could lead to a bias in the hazard evaluation.

Description: We used intensity information from five calibration earthquakes to estimate an intensity attenuation model for the Rio Grande rift region (encompassing west Texas, New Mexico, and southern Colorado). The attenuation model lies between similar models developed for the Basin and Range Province and central and eastern North America. Analysis of two test earthquakes occurring in 1931 and 2014 validated that the intensity attenuation relation adequately predicted the events’ magnitudes and epicenters. We then analyzed intensity information for nine historical (1906–1960) earthquakes to determine their magnitudes and epicenters. Our results indicate that the largest earthquakes of the 1906 Socorro, New Mexico, sequence had intensity magnitudes ( M I ) 5.7–5.9 and may represent north-to-south migration of seismicity associated with the Socorro magma body. Moderate earthquakes in 1935 and 1960 also are associated with the magma body. The 1938 Arizona–New Mexico border earthquake sequence occurred about 50 km northeast of the ongoing 2014 Arizona–New Mexico border sequence. The 17 September earthquake of the 1938 sequence had an M I (4.1) that was about 1.0 units less than that of the 29 June 2014 Arizona–New Mexico event ( M I  4.9).

Description: We investigated the hypocenter distribution along the Nankai trough off the Kii Peninsula, Japan, by using data from both ocean-bottom and land-based seismic networks. Because seismic velocity structures differ greatly below land and ocean, we used a 3D velocity model based on a structural model of the Philippine Sea plate (PHS), which provides much more accurate estimations of source locations than 1D velocity models derived from either onshore or ocean-bottom seismic data alone, especially for sources between the coast and the trough axis. We identified intensive seismic activity below the axis of the Nankai trough, which we interpreted to be aftershocks of the 2004 Off the Kii Peninsula earthquakes ( M JMA  7.1, 7.4, and 6.5), but found much less seismic activity along the subducting PHS. The earthquake sources below the trough axis lie on dipping planes within the PHS, from which we inferred that a fracture zone is developing within the PHS. Our estimated focal mechanisms for these earthquakes showed that their P axes were oriented north–south to northeast–southwest, similar to those of the 2004 events, which were rotated clockwise by 45°–90° from the northwest–southeast direction of convergence between the PHS and the Eurasian plates. We consider that the fracture zone represents a boundary between the PHS and the Izu microplate, which are converging in a north–south direction, and that the 2004 earthquakes and subsequent seismic activity were caused by the collision of these plates.

Description: A Monte Carlo approach to probabilistic seismic-hazard analysis is developed for a case of induced seismicity associated with a compacting gas reservoir. The geomechanical foundation for the method is the work of Kostrov (1974) and McGarr (1976) linking total strain to summed seismic moment in an earthquake catalog. Our Monte Carlo method simulates future seismic hazard consistent with historical seismic and compaction datasets by sampling probability distributions for total seismic moment, event locations and magnitudes, and resulting ground motions. Ground motions are aggregated over an ensemble of simulated catalogs to give a probabilistic representation of the ground-motion hazard. This approach is particularly well suited to the specific nature of the time-dependent induced seismicity considered. We demonstrate the method by applying it to seismicity induced by reservoir compaction following gas production from the Groningen gas field. A new ground-motion prediction equation (GMPE) tailored to the Groningen field has been derived by calibrating an existing GMPE with local strong-motion data. For 2013–2023, we find a 2% chance of exceeding a peak ground acceleration of 0.57 g and a 2% chance of exceeding a peak ground velocity of 22 cm/s above the area of maximum compaction. Disaggregation shows that earthquakes of M w  4–5, at the shortest hypocentral distances of 3 km, and ground motions two standard deviations above the median make the largest contributions to this hazard. Uncertainty in the hazard is primarily due to uncertainty about the future fraction of induced strains that will be seismogenic and how ground motion and its variability will scale to larger magnitudes.

Description: At the southern Hikurangi margin, New Zealand, we use salt marsh stratigraphy, sedimentology, micropaleontology, and radiocarbon dating to document evidence of two earthquakes producing coseismic subsidence and (in one case) a tsunami over the past 1000 yrs. The earthquake at 520–470 yrs before present (B.P.) produced 0.25±0.1 m of subsidence at Big Lagoon. The earthquake at 880–800 yrs B.P. produced 0.45±0.1 m of subsidence at Big Lagoon and was accompanied by a tsunami that inundated ≥360 m inland with a probable height of ≥3.3 m. Distinguishing the effects of upper plate faulting from plate interface earthquakes is a significant challenge at this margin. We use correlation with regional upper plate paleoearthquake chronologies and elastic dislocation modeling to determine that the most likely cause of the subsidence and tsunami events is subduction interface rupture, although the older event may have been a synchronous subduction interface and upper plate fault rupture. The southern Hikurangi margin has had no significant ( M 〉6.5) documented subduction interface earthquakes in historic times, and previous assumptions that this margin segment is prone to rupture in large to great earthquakes were based on seismic and geodetic evidence of strong contemporary plate coupling. This is the first geologic evidence to confirm that the southern Hikurangi margin ruptures in large earthquakes. The relatively short-time interval between the two subduction earthquakes (~350 yrs) is shorter than in current seismic-hazard models. Online Material: Historical accounts, description of vertical deformation, core names, foraminifera census and abundance, diatom census, modern analog samples, map of cores collected, stratigraphic correlation diagram for all cores, and detailed core logs.

Description: This research presents the power spectral density (PSD) of double-frequency (DF) microseisms of 13 continuous single-point long-term ambient noise recordings (LTRs) at five inland and two coastal locations selected in Mississippi and Louisiana states and 234 single-point short-term ambient noise recordings (STRs) in northern Mississippi. By correlating PSD of LTRs with the simultaneous ocean data (including significant ocean wave frequency, significant ocean wave height, ocean wind speed, and above-ocean atmosphere pressure) of the Atlantic Ocean and Gulf of Mexico, as well as local atmosphere pressure and wind speed, DF microseisms observed in northern Mississippi were shown to be shaped by a combined impact of both wave climates of the Atlantic Ocean and Gulf of Mexico. Particle motion analysis and calculation of vibration angle defined separately for LTRs and STRs strengthen this conclusion. The DF and PSD level at DF of STR plots in the horizontal direction versus unconsolidated sediment thickness show significant differences from the plots in the vertical direction, which indicates that the shear-wave resonance in thick sediments modifies the DF microseisms more obviously in the horizontal than in the vertical direction.

Description: The quality factor of coda ( Q c ) waves has been estimated by using single backscattering and single isotropic scattering models. The earthquakes used were recorded by three permanent and one temporary network located in the central and eastern Alborz, Iran. The database was composed of 746 local earthquakes with local magnitude from 1.1 to 5.7. The estimated Q c has been found to be similar for lapse times greater than twice the S -wave travel time (2 t S ) for both methods. The estimated Q c for central frequencies 〈1.0 Hz shows less frequency dependency compared with the higher frequencies. By using a Q 0 f n relation, the average frequency dependence of Q c for the whole area has been estimated as 59 f 1.03 , 69 f 0.97 , 78 f 0.97 , 105 f 0.93 , 123 f 0.89 , 159 f 0.79 , and 203 f 0.68 for central lapse times 30, 40, 50, 65, 85, 110, and 155 s, respectively. We found the value of Q 0 decreases at an average depth of 78 km, which may be the result of high dissipating media at this depth. The average Q c values, estimated for central and eastern Alborz and their frequency-dependent relationships are similar to those of tectonically active regions.

Description: The Central Java region is one of the most seismically active regions in Indonesia. Each year, the region experiences an average of more than 20 medium-to-large magnitude earthquakes. Hence, reliable hazard analysis is necessary for the region, and we undertook this study in order to conduct a probabilistic seismic-hazard analysis to estimate and map peak ground acceleration (PGA) and spectral response at 0.2 and 1 s periods, with 10% probability of exceedance in 50 years corresponding to the return period of 475 years. Maps presented in this study are intended for regional purposes only and may be useful for emergency response planning and urban development. The database used in this study is compiled from the Indonesian Meteorological, Climatological, and Geophysical Agency, the U.S. Geological Survey, and the Incorporated Research Institutions for Seismology. The compiled catalog covers an area between latitude 5°–12° S and longitude 105°–115° E and includes moment magnitude 5 and greater from 1900 to February 2011. We used a standard logic-tree approach that included systematic allowances for various seismicity models. Because a region-specific empirical ground-motion model is lacking, we used Next Generation Attenuation ground-motion relations. We calculated PGA and spectral response at 0.2 and 1 s periods for all cities across Central Java. We found that the city of Pati is subject to the highest seismic hazard with a PGA of 0.45 g , and the city of Kendal has the lowest hazard with a PGA of 0.13 g . This study provides a basis upon which to design maps for building codes and emergency planning.

Description: Tectonic tremor has previously been observed along two major transform faults: the San Andreas fault (SAF) and the Alpine fault (AF); and we extend the search for tectonic tremor to another transform fault, the North Anatolian fault (NAF). We investigate a two-year-long temporary broadband seismic deployment on an ~400 km long NAF segment in central Turkey. The central NAF network has stations within a few kilometers of the fault. Although the station spacing is larger than for the SAF and AF networks, we still expect to be able to observe coherent tremor at several stations, if it occurs in similar amounts as elsewhere. We search for tremor triggered by the surface waves of regional and teleseismic earthquakes but do not observe any tremor associated with the passage of surface waves. Next, we search for ambient tremor and observe occasional tremor-like signals, but the signals are not coherent between stations. Thus, we cannot identify any unambiguous tremor episodes and suggest that if tremor occurs along the central NAF, it occurs at a lower amplitude and/or rate than along the SAF or AF.

Description: Probabilistic seismic-hazard analysis (PSHA) is the current tool of the trade used to estimate the future seismic demands at a site of interest. A modern PSHA represents a complex framework that combines different models with numerous inputs. It is important to understand and assess the impact of these inputs on the model output in a quantitative way. Sensitivity analysis is a valuable tool for quantifying changes of a model output as inputs are perturbed, identifying critical input parameters, and obtaining insight about the model behavior. Differential sensitivity analysis relies on calculating first-order partial derivatives of the model output with respect to its inputs; however, obtaining the derivatives of complex models can be challenging. In this study, we show how differential sensitivity analysis of a complex framework such as PSHA can be carried out using algorithmic/automatic differentiation (AD). AD has already been successfully applied for sensitivity analyses in various domains such as oceanography and aerodynamics. First, we demonstrate the feasibility of the AD methodology by comparing AD-derived sensitivities with analytically derived sensitivities for a basic case of PSHA using a simple ground-motion prediction equation. Second, we derive sensitivities via AD for a more complex PSHA study using a stochastic simulation approach for the prediction of ground motions. The presented approach is general enough to accommodate more advanced PSHA studies of greater complexity.

Description: We present a method to estimate precise relative magnitudes using cross correlation of seismic waveforms. Our method incorporates the intercorrelation of all events in a group of earthquakes, as opposed to individual event pairings relative to a reference event. This method works well when a reliable reference event does not exist. We illustrate the method using vertical strike-slip earthquakes located in the northeast Pacific and Panama fracture zone regions. Our results are generally consistent with the Global Centroid Moment Tensor catalog, which we use to establish a baseline for the relative event sizes. Online Material: Supplementary description and formulation of uncertainty, and tables of relative magnitudes.

Description: The 2004 M w  6.0 Parkfield, California, earthquake took place in a very well-instrumented area, producing a substantial quantity of high-quality near-field recordings. Taking advantage of the rare luxury of having a large number of near-field ground-motion recordings distributed around the fault zone and the availability of various slip models as well as an Earth structure model of the region, we study the effects of various kinematic rupture parameters to derive implications for strong ground motion simulation in engineering applications. We model the 3D wave propagation resulting from this earthquake using the 3D staggered-grid finite-difference method. Using a grid spacing of 100 m in our fourth-order explicit finite-difference code, we could properly resolve frequencies of up to 1 Hz with a minimum of eight grids per wavelength for shear waves, except in the immediate vicinity of the fault where fault-trapped waves dominate the records. We assess the effects of various simulation parameters such as slip model, rise time (constant or variable), rupture velocity, and the earth model (1D versus 3D) on the resulting waveforms. We also investigate the distribution of engineering parameters such as peak ground velocities, peak ground displacements, and spectral accelerations at specific periods on the Earth’s surface. An outstanding feature is that at high frequencies fault-normal components near the edge of fault segments dominate the ground-motion field. Fault-parallel components are dominated by lower frequencies. The difference between fault-parallel and fault-normal components is clearly observed in such engineering parameters as peak ground velocity and peak ground displacement.

Description: The magnitude conversion problem, usually concerning the estimation of proxies of moment magnitude M w from local ( M L ) and teleseismic ( M s and m b ) magnitude estimates, was addressed by a number of recent articles. In most of them, the general orthogonal regression (GOR) method is employed; in place of the ordinary least squares (OLS), owing to the fact that the errors of local and teleseismic magnitudes are not negligible with respect to those of M w . In the last two years, researchers proposed a modified GOR (MGOR) procedure that claimed to achieve unbiased estimates of M w using an estimator of the true value of the independent variable ( x t ) in place of the observed value ( X obs ) in regressed equations. In this article, we demonstrate both theoretically and experimentally that (a)  x t coincides on average with X obs , (b) the proposed procedure to calculate x t is biased by the choice of using the OLS regression method to fit the linear relationship between x t and X obs , and (c) the claimed better fit of MGOR proxies with observed data is due to the use of goodness-of-fit estimators that neglect the error of the independent variable. In particular, we show the regression method that best minimizes such estimators is the OLS, which assumes that the error of the independent variable is negligible. This, however, does not mean that the OLS is the better approach for computing conversion equations between different magnitudes; because, owing to the presence of errors of the independent variable, it is simply not applicable to magnitude conversion as well as the MGOR procedure.

Description: We investigate the influence of building height on the ability of people to feel earthquakes and observe that, in an urban area, short and tall buildings reach different levels of excitation. We quantify this behavior by analyzing macroseismic reports collected from individuals through the Internet; we focus on elastic regime transitory effects of recent earthquakes in Italy in the local magnitude ( M L ) range of 3–5.9. We find a maximum difference of 0.6 intensity units between the top floors of tall (7–10 stories) and short (1–2 stories) buildings at the highest considered magnitudes. As expected, tall buildings experience greater shaking than short buildings during large earthquakes at large source distances. However, we observe the opposite behavior at close distances when the M L is 〈3.5. These results can be explained by considering the different spectra radiated by small and large earthquakes and the different fundamental mode resonances of buildings (i.e., shorter buildings have higher resonance frequencies and vice versa). Using idealized building models excited by real acceleration time histories, we compute synthetic accelerograms on the top floors of short and tall buildings and confirm the trend of the observed differences in felt intensities.

Description: SSA members are invited to vote for members of the Board of Directors in the 2016 election. The candidates’ statements are presented below, in the order they were received from the candidates. The election is open for voting until 5 p.m. PST on Friday, 8 January 2016. The voting system is easier than ever, and SSA strongly urges members to participate in the Society’s future by casting their ballots. To vote, go to the Members’ Area of the SSA website ( www.seismosoc.org ), and click on the "Vote Now" box after you have completed your 2016 member renewal. (Please note, only the votes of members current in their 2016 dues will be tallied.) Look for reminders to vote from SSA to come throughout the months of the election ( membership@seismosoc.org or election@seismosoc.org ) and from Election America ( SSAvote@election-america.com ). For assistance, please contact election@seismosoc.org or phone 510-525-5474.

Description: In this article, we implement a web questionnaire (available in Spanish at the www.fct.uanl.mx , last accessed March 2014, as Encuesta sismo ) to gather citizens’ observations on felt earthquakes in an area of northeastern Mexico. We generated a seismic intensity map due to the fact that some events from the October 2013 to March 2014 seismic sequence (1.9≤ M c ≤4.5) were recorded and felt in the region. This sequence occurred in the central area of the state of Nuevo León. The data obtained from this questionnaire and by interviewing people living near the epicentral area are useful for a rapid postearthquake evaluation. This is important because the maximum intensity values were of V–VI near the epicentral area. Finally, the attenuation curves obtained from our study proved to be similar to those for central and eastern United States.

Description: Using template waveforms from aftershocks of the Wenchuan earthquake (12 May 2008, M s  7.9) listed in a global bulletin and continuous data from eight regional stations, we detected more than 6000 additional events in the mainshock source region from 1 May to 12 August 2008. These new detections obey Omori’s law, extend the magnitude of completeness downward by 1.1 magnitude units, and lead to a more than fivefold increase in number of known aftershocks compared with the global bulletins published by the International Data Centre and the International Seismological Centre. Moreover, we detected more M 〉2 events than were listed by the Sichuan Seismograph Network. Several clusters of these detections were then relocated using the double-difference method, yielding locations that reduced travel-time residuals by a factor of 32 compared with the initial bulletin locations. Our results suggest that using waveform correlation on a few regional stations can find aftershock events very effectively and locate them with precision.

Description: Few studies have been conducted on the variance of scattering ( ) and intrinsic attenuation ( ) with depth in the crust. Furthermore, these values, routinely estimated using multiple lapse time window analysis (MLTWA), were seriously affected by different earthquake depths. Based on earthquakes recorded by dense seismic networks in South Korea, we used the MLTWA method on single or small clusters of events with similar depths. The depths of 54 earthquakes, relocated using seven velocity models, provide a typical seismogenic layer with the brittle–plastic transition (BPT) depth at 11 km, which correlated well with the seismicity of Korea. The depth was also used for the theoretical model based on the direct-simulation Monte Carlo method. As the result of MLTWA, events with shallow focal depths exhibit higher correlated with dense scatter, whereas those with deeper focal depths exhibit lower . This depth dependency of the value is indicated by the significant difference between the upper and lower parts of the BPT depth in the seismogenic layer. We also found that values do not show depth dependency, whereas values do. Thus, this study demonstrates for the first time that the crustal depth dependency of total ( ) attenuation originates from rather than from . The approach using single or few events may be helpful for a regional study of and in seismically inactive regions for which insufficient data exist and may provide insight into the seismogenic layer related to potential seismic hazards. Online Material: Tables of residuals and range of multiple lapse time window analysis (MLTWA) parameters and Q –1 values for studied events.

Description: Since the inception of the borehole seismic array deployed by the Central Weather Bureau (CWB) in Taiwan in recent years, a large quantity of strong-motion records have been accumulated from frequently occurring earthquakes around Taiwan that provide the opportunity to investigate the spectral decay parameter kappa ( ) and to understand further the site effects of seismic stations. In this study, we used 133 earthquakes recorded at 30 borehole seismic arrays. Each array includes two force-balance accelerometers, one at the surface and the other inside the borehole. Based on the regression analysis between -value and hypocentral distance for each surface–borehole station pairs, the resulting 0 derived from surface stations are higher than results from borehole stations. The estimated 0 -values are found to range from 0.032 to 0.097 s at surface and 0.012 to 0.078 s in borehole. In comparison with a study of site corrections for earthquake magnitude determination, these higher 0 -values associated with negative station corrections can correspond to the effect of soil conditions. To evaluate station corrections of borehole seismic array, we collected records from the cosite stations of Taiwan Strong-Motion Instrumentation Program (TSMIP) and Central Weather Bureau Station Network (CWBSN) and then derived a linear relationship between the 0 -values and station corrections. Finally, both resulting station corrections and 0 -values reveal high coherence in local site conditions.

Description: The frequency content of strong ground motions from subduction slab earthquakes differs significantly from that of ground motions produced by other categories (tectonic locations: shallow crustal, upper mantle, and subduction interface) of earthquakes in subduction zones. In the last two decades, a large number of records from subduction slab events have been obtained in Japan. We present a ground-motion prediction equation (GMPE) for this category of earthquakes. We used a large dataset from reliably identified slab events up to the end of 2012. The GMPEs were based on a set of simple geometric attenuation functions, site classes were used as site terms, and nonlinear site amplification ratios were adopted. A bilinear magnitude-scaling function was adopted for large earthquakes with moment magnitude M w ≥7.1, with the scaling rates for large events being much smaller than for the smaller events. A magnitude-squared term was used for events with M w 〈7.1 as well as the bilinear magnitude-scaling function. We also modeled the effect of volcanic zones using an anelastic attenuation coefficient applied to a horizontal portion of the seismic-wave travel distance within possible volcanic zones. We found that excluding the records from sites with inferred site classes improved the model goodness of fit. The within-event residuals were approximately separated into within-site and between-site residuals, and the corresponding standard deviations were calculated using a random effects model. The separation of within-event residuals into within-site and between-site components allows for the possibility of adopting different standard deviations for different site classes in a probabilistic seismic-hazard analysis if desired. Online Material: Figures showing the distribution of between-event residuals with respect to magnitude and fault-top depth and the distribution of within-event residuals with respect to magnitude and source distance.

Description: In this article, ground-motion prediction equations (GMPEs) based on the horizontal components of the strong-motion records from shallow crustal and upper-mantle earthquakes in Japan are presented. We assembled a large dataset from earthquakes with a moment magnitude ( M w ) over 4.9 and a reliable earthquake category (the tectonic location of earthquakes) up to the end of 2012. The GMPEs were based on a set of simple geometric attenuation functions. A bilinear magnitude-scaling function hinged at M w  7.1 was adopted, with the scaling rates for large events being much smaller than those for the smaller events. Site classes based on site period were used as site terms, and nonlinear site terms were included. We modeled the effect of volcanic zones using an anelastic attenuation coefficient applied to a horizontal portion of the seismic-wave travel distance within volcanic zones. Most strong-motion records in our dataset are from stations with a measured shear-wave velocity profile down to engineering bedrock. A small number of records are from stations with inferred site classes using the response spectral ratio of the horizontal-to-vertical components or geologic description of the surface soil layers. We tested the effect of site information quality by comparing the goodness-of-fit parameters from the model with and without the sites with inferred site classes. Our results suggest that the site information quality made a significant difference for spectral periods over 0.7 s, that is, the exclusion of sites with inferred site classes improves the model fit significantly. The within-event residuals were approximately separated into within-site and between-site components, and the corresponding standard deviations were calculated. The approximate separation allows for the possibility of adopting different standard deviations for different site classes in a probabilistic seismic-hazard analysis if desired. Online Material: References for fault rupture plane models, earthquake records and volcanic zones information, illustration of site information quality effect, standard deviations for between-event, within-event, between-site and within-site residual, and the distribution of between-event and within-event residuals.

Description: We investigate near-field ground-motion variability by computing the seismic wavefield for five kinematic unilateral-rupture models of the 1992 M w  7.3 Landers earthquake, eight simplified unilateral-rupture models based on the Landers event, and a large M w  7.8 ShakeOut scenario. We include the geometrical fault complexity and consider different 1D velocity–density profiles for the Landers simulations and a 3D heterogeneous Earth structure for the ShakeOut scenario. For the Landers earthquake, the computed waveforms are validated using strong-motion recordings. We analyze the simulated ground-motion data set in terms of distance and azimuth dependence of peak ground velocity (PGV). Our simulations reveal that intraevent ground-motion variability is higher in close distances to the fault (〈20 km) and decreases with increasing distance following a power law. This finding is in stark contrast to constant sigma-values used in empirical ground-motion prediction equations. The physical explanation of a large near-field is the presence of strong directivity and rupture complexity. High values of occur in the rupture-propagation direction, but small values occur in the direction perpendicular to it. We observe that the power-law decay of is primarily controlled by slip heterogeneity. In addition, , as function of azimuth, is sensitive to variations in both rupture speed and slip heterogeneity. The azimuth dependence of the ground-motion mean μ ln(PGV) is well described by a Cauchy–Lorentz function that provides a novel empirical quantification to model the spatial dependency of ground motion. Online Material: Figures of slip distributions, residuals to ground-motion prediction equations (GMPEs), distance and azimuthal dependence, and directivity predictor of ground-motion variability for different source models.

Description: A new ground-motion prediction equation (GMPE) model for central and eastern North America (CENA) is presented. The Graizer 2016 (G-16) model is based on the Next Generation Attenuation-East (NGA-East) database for this horizontal peak ground acceleration and 5% damped pseudospectral acceleration RotD50 component ( Goulet et al. , 2014 ). The CENA database is not sufficient for creating purely empirical GMPE with recordings covering mostly a range of moment magnitudes M 〈6.0 and a limited number of near-fault recordings. The functional forms of the G-16 model are derived from filters representing a particular physical phenomenon affecting the seismic-wave radiation from the source, following the approach developed by Graizer and Kalkan (2007 , 2009 , and 2011 ) for active tectonic environment. Main changes in the functional forms for CENA relative to the western United States model ( Graizer and Kalkan, 2015 ) are a shift of maximum frequency of the acceleration response spectrum (RS) toward higher frequencies and an increase in RS amplitudes at high frequencies. The developed site correction is based on multiple runs of representative V S 30 profiles through SHAKE-type equivalent-linear codes. Site amplifications are calculated relative to the hard-rock definition used in nuclear industry ( V S =2800 m/s). The number of model predictors is limited to a few measurable parameters such as moment magnitude M , closest distance to fault rupture plane R rup , V S 30 , and anelastic attenuation factor Q 0 . Incorporating Q 0 as an input parameter allows adjustments based on the regional crustal properties. The model is applicable for the stable continental regions and covers the following range: 4.0≤ M ≤8.5, 0≤ R rup ≤1000 km, 450≤ V S 30 ≤2800 m/s, and frequencies 0.1≤ f ≤100 Hz.

Description: Characterizing the seismicity of Novaya Zemlya and the surrounding Arctic seas requires accurate event-location estimates. Low-magnitude events in this region are currently observed only by a small number of stations in the European Arctic, with a large azimuthal gap, making the accuracy of regional velocity models all the more important. Regional travel-time calibration is difficult given the scarcity of sufficiently well-constrained events. On 11 October 2010, a magnitude 4.5 event occurred close to the northern tip of Novaya Zemlya. This event is significant in that it is the first event in this region to have been recorded both on the relatively recent regional networks and arrays, and also teleseismically with good azimuthal coverage. We examine how well we can constrain the location and origin time using only teleseismic phases. Using only first teleseismic P arrivals, we constrain the epicenter to approximately 76.25° N and 64.75° E but with no depth resolution. Clear depth phases, notably on stations in the southern United States, indicate a depth between 9 and 15 km. This independent hypocenter and origin time estimate allow evaluation of regional phase travel-time prediction using different models. The predicted Sn travel time appears to cause the greatest variability in regional location estimates. The 3D Regional Seismic Travel Times models provide excellent Pn travel-time estimates for Barents Sea paths but may slightly overestimate Sn travel times from this source region. A modified regional 1D velocity model is defined, which best predicts Pn and Sn observations at multiple stations up to 15°. The significance of the regional travel-time models for estimating location is demonstrated for a low-magnitude event on or close to the northern island of Novaya Zemlya in March 2014, recorded with a satisfactory signal-to-noise ratio at only four stations.

Description: Dynamic slip pulse propagation along a material interface is of great interest because many faults are known to lie along material interfaces and such interfaces may cause pulse-like ruptures. This subject has been extensively studied numerically over the last two decades. It has not, however, been studied very thoroughly from an analytical standpoint, although analytical studies would complement numerical ones. In particular, an analytical solution for removing stress singularities has not yet been obtained, even after an asymptotic analysis. In this article, we employ three physically plausible conditions in our theoretical modeling: (1) arbitrary propagation speeds in the sub-Rayleigh range, (2) a slip-weakening friction law, and (3) boundedness of stress. We can construct an analytical solution under these conditions, and as a result of our parameter study, we determine the dependence of slip-weakening distance and the ratio of process zone size to pulse length on rupture direction and velocity. These results enable us to discuss a mechanism for limiting rupture velocity and estimating the slip-weakening distance in seismic inversion analyses.

Description: Globally, one of the largest intraplate earthquakes of M w  7.7 occurred on 26 January 2001 in the Kachchh rift basin (KRB), western India. The continuing long aftershock sequence over decades has generated much debate on the seismogenic fault(s). We have analyzed more than 10,000 aftershocks ( M w 〉1.0) recorded by a 50-station broadband network in the region during 2006–2014. A total of 834 aftershocks ( M w 〉2.4), each recorded by at least eight broadband seismic stations with a minimum of eight P and six S phases, are relocated in this study by double-difference tomography (tomoDD) method. The relocated aftershocks and velocity images reveal a near-vertical or steeply south-dipping deeper structure as the source zone of the mainshock and aftershocks; the structure correlates well with the geologically mapped South Wagad fault (SWF). Among the other geologically known faults, the Kachchh Mainland fault (KMF) and the Gedi fault (GF) are also well identified in the seismic sections. Further, fault-plane solutions of 109 aftershocks having M w ≥3.5 corroborate well with the known faults. The geological model and seismological observations suggest that the SWF overstepped the KMF and intersects it at depth. The intersecting fault zone is the source area for the deeper (10–35 km) reverse faulting earthquakes in the KRB. At the fault end of the SWF, a heterogeneous velocity structure is imaged, which is attributed to a fluid-filled rock matrix that triggered the mainshock. On the other hand, the GF is reported to be a later-activated fault to the north of SWF; it generated some shallower aftershocks (0–20 km) mostly by strike-slip mechanisms.

Description: Observations show the appearance of abnormal b -values prior to a mainshock. The precursor time T of b -value anomalies prior to a forthcoming mainshock is related to the magnitude M of the event in an equation: log( T )= q + rM , in which q and r are two constants. In this study, implications of this equation will be explained. In addition, the mechanism causing b -value anomalies prior to a mainshock will be explored. From numerical simulations based on the 1D Knopoff–Burridge spring-slider model, Wang (1995) found a power-law correlation between b and s , in which the parameter s is the ratio of the spring constant ( K ) between two sliders to that ( L ) between a slider and the moving plate. The power-law correlations are b ~ s –2/3 for the cumulative frequency and b ~ s –1/2 for the discrete frequency. Because L of a source area is almost constant for a long-time period, b directly relates to K . Smaller (larger) K results in a higher (lower) b -value. Wang (2012) found , in which A and V P are the areal density and P -wave velocity of a fault zone, respectively. Experimental results show that V P is strongly influenced by the water saturation in rocks. The water saturation in the source area varies with time, thus leading to a temporal variation in V P as well as K . This results in the temporal variation in b -values.

Description: We presented a set of ground-motion prediction equations (GMPEs) for the horizontal components of strong-motion records from subduction interface events in Japan. We assembled and processed in a consistent manner a large set of strong-motion records from reliably identified subduction interface events up to the end of 2012. The GMPEs were based on a set of simple geometric attenuation functions, and site class was based on site period as the site parameter. We adopted a bilinear magnitude-scaling function hinged at M w  7.1 and found that the magnitude-scaling rate for large events is much smaller than that for smaller events. To reliably determine the magnitude-scaling rate for events with M w ≥7.1, we used a set of strong-motion records obtained since 1968 to increase the number of records from large events. A small number of strong-motion records are from recording stations with inferred site classes using the response spectral ratio of the horizontal-to-vertical components or a geological description of the surface soil layers. The effect of site information quality for subduction interface events was examined using a goodness-of-fit parameter from a dataset with or without the sites having an inferred site class. The site information quality made a significant difference at all spectral periods, because the model fit improved significantly when the sites with inferred classes were excluded. We modeled the effect of volcanic zones using an anelastic attenuation coefficient applied to the horizontal portion of the seismic-wave travel distance within a set of assumed volcanic zones. The within-event residuals were approximately separated into within-site and between-site components, and the corresponding standard deviations were calculated using a random effects model. The between-site standard deviations vary significantly among site classes and with spectral periods. Online Material: Figures showing distributions of between-event and within-event residuals.

Description: The recording on high-resolution broadband seismic networks of several great interface subduction earthquakes during the last decade provide an excellent opportunity to extend source-scaling relations to very large magnitudes and to place constraints on the potential range of source parameters for these events. At present, there is a wide range of uncertainty in the median rupture areas predicted for any given seismic moment by current relationships between magnitude and rupture area for subduction interface earthquakes. Our goal is to develop an updated set of earthquake source-scaling relations that will reduce this current large degree of epistemic uncertainty and improve the accuracy of seismic-hazard analysis and the prediction of the strong-motion characteristics and tsunamis of future subduction earthquakes. To achieve this goal, we compiled a database including slip models of interface earthquakes that occurred worldwide with moment magnitudes ranging from M  6.75–9.1. We characterized the seismic sources based on well-established criteria to estimate the asperity areas as well as the average slip on the faults, and we used these parameters to compute an updated set of magnitude scaling relations of the various characteristics of the fault. Additionally, we followed an alternative approach to quantifying slip models for use in developing characteristic slip models of future earthquakes. This involved analyzing the 2D Fourier transforms of the slip functions in the compiled database and deriving a wavenumber spectral model of the slip distribution.

Description: We examine the scaling of spectral properties of 122 local earthquakes (2.6〈 M L 〈5.5) recorded by a network of 10 broadband seismic stations during the period January 2001–November 2007 in northeast India. The spectral (low-frequency plateau and corner frequency) and source (static stress drop, radiated energy, and radiation efficiency) parameters are obtained assuming an omega-square source model. The source parameters are obtained from the displacement spectra corrected for frequency-dependent attenuation and site effects, and limited frequency bandwidth. The well-resolved estimates of these parameters, corresponding to corner frequencies within the maximum frequency resolution limit, are included in the analysis. We discuss the self-similar scaling by introducing a nondimensional parameter that is proportional to stress drop independent of any particular fault geometry and by considering the measurement bias. For the events used in this study, the value of C r is close to 2.0, a value expected for circular crack model and self-similar source scaling. However, the relatively large uncertainties due to earthquake selection bias and recording bandwidth limitation suggest caution in drawing conclusions from these findings. The events are grossly characterized by low and almost constant value of radiation efficiency and positive overshoot corresponding to an increase in relative dynamic strength, suggesting the importance of energy dissipation during the rupture process. Although the scaling of radiated energy and stress drop, as obtained here, takes into account as much as possible the effects of finite bandwidth, attenuation, and site corrections, the limited event selection may strongly bias it. An improvement over the present scaling is suggested with an improved seismic network in the region and also with the use of a stable empirical Green’s function approach for source parameter estimation.

Description: Although the time-averaged shear-wave velocity down to 30 m depth ( V S 30 ) can be a proxy for estimating earthquake ground-motion amplification, significant controversy exists about its limitations when used as a single parameter for the prediction of amplification. To examine this question in absence of relevant strong-motion records, we use a range of different methods to measure the shear-wave velocity profiles and the resulting theoretical site amplification factors (AFs) for 30 sites in the Newcastle area, Australia, in a series of blind comparison studies. The multimethod approach used here combines past seismic cone penetrometer and spectral analysis of surface-wave data, with newly acquired horizontal-to-vertical spectral ratio, passive-source surface-wave spatial autocorrelation (SPAC), refraction microtremor (ReMi), and multichannel analysis of surface-wave data. The various measurement techniques predicted a range of different AFs. The SPAC and ReMi techniques have the smallest overall deviation from the median AF for the majority of sites. We show that V S 30 can be related to spectral response above a period T of 0.5 s but not necessarily with the maximum amplification according to the modeling done based on the measured shear-wave velocity profiles. Both V S 30 and AF values are influenced by the velocity ratio between bedrock and overlying sediments and the presence of surficial thin low-velocity layers (〈2 m thick and 〈150 m/s), but the velocity ratio is what mostly affects the AF. At 0.2〈 T 〈0.4 s, the AFs are largely controlled by the surficial geology of a particular site. AF maxima are the highest in the hard classes, which is the inverse of the findings used in the Australian Building Code. Only for T 〉0.5 s do the amplification curves consistently show higher values for soft site classes and lower for hard classes.

Description: Empirical relationships between the macroseismic intensity and the ground-motion parameters for the Himalayan region are derived in this study. A strong-motion database from 21 moderate-to-large earthquakes, along with their corresponding macroseismic intensity, is considered. All the intensity values are inferred from isoseismal maps and earthquake damage reports and then converted to the modified Mercalli intensity (MMI) scale. An orthogonal regression analysis is used to find the best correlation between MMI and peak ground acceleration (PGA), peak ground velocity (PGV), and pseudospectral acceleration (PSA) at 0.3, 1.0, 2.0, and 3.0 s to accommodate the uncertainty in the regression coefficients. In addition to the ground-motion parameters, the MMI is related to other potential independent variables, including the moment magnitude, the hypocentral distance, and the 30-m average shear-wave velocity ( V S 30 ). The study shows that site effect is noticed predominantly in the MMI–PGA relationship for a hypocentral distance of more than 200 km. When relating MMI with PGV, PSA 0.3 s , PSA 1.0 s , PSA 2.0 s , and PSA 3.0 s , however, the contribution of site effects to the correlation is negligible. To eradicate the site effect in the PGA–MMI relationship, the derived empirical relationship is modified, based on the statistical analysis of MMI observed and MMI predicted, with or without including V S 30 as a potential independent variable. Furthermore, the developed regression models are verified using several statistical tests, the F -test, the t -test, the Durbin–Watson test, and the Breusch–Pagan test. Additionally, the Euclidean distance concept is evaluated in the study. It was concluded that the PGA is a good indicator for deriving the MMI value in the Himalayan region, but that one should use site-specific MMI versus PGV and MMI versus PSA relationships to predict reliable parameters.

Description: We present an extensive analysis of the quantitative impact of the nonlinear soil behavior on site response at 174 sites of the Japanese Kiban–Kyoshin (KiK-net) network. The nonlinear to linear site-response ratio (RSR NL–L ) is calculated by comparing the surface/downhole Fourier spectral ratio for strong events and for weak events. Three thresholds of surface peak ground acceleration (PGA) are tested to characterize the strong events: 100, 200, and 300 cm/s 2 , whereas weak events correspond to surface PGA in the 0.1–25 cm/s 2 range. This ratio exhibits a typical shape; with a low-frequency part above 1 and a high-frequency part generally below 1, separated by a transition zone around a site-dependent frequency labeled f NL (characterized by RSR NL–L =1). The average maximum amplitudes of RSR NL–L are 1.4, 1.5, and 1.6, and the minimums are 0.6, 0.5, and 0.5 for PGA thresholds 100, 200, and 300 cm/s 2 , respectively, showing that nonlinear soil behavior results in significant site-response modifications even for moderate PGA values of 100 cm/s 2 . The f NL value exhibits a satisfactory correlation with site classifications based on either V S 30 (travel-time averaged shear-wave velocity over the top 30 m) or f 0 (site fundamental frequency): f NL decreases when either V S 30 or f 0 decreases. In addition, the amount of the low-frequency amplification increase depends on V S 30 and reaches a maximum of 1.6 for high V S 30 soil classes associated with shallow thin soft-soil layer underlain by stiff substratum. The average high-frequency decrease is about 0.5 for all soil classes defined from either V S 30 or f 0 ; for a few sites, however, this decrease is replaced by an increase as reported in previous studies, in relation with water contents and pore-pressure issues. The increase of amplification below f NL is found to be a quasi-systematic consequence of nonlinear soil behavior, which should be emphasized, because it can reach up to 1.6 for high V S 30 sites. Online Material: Figures of site-response ratio (RSR) curves and tables of site characteristics.

Description: Studies have shown that random vibration theory (RVT) site-response analysis predicts site amplification at the natural site frequencies that are systematically larger than the results obtained from time series (TS) analysis using a suite of input TS. A critical part of the RVT approach is the peak factor, defined as the ratio of the peak to root mean square (rms) value of a signal. This study investigates the influence of different peak factor models on the site amplification estimated by RVT site-response analysis. It is shown that the use of the Vanmarcke (1975) peak factor model rather than the Cartwright and Longuet-Higgins (1956) peak factor model predicts site amplification in better agreement with those predicted by TS analysis, although some differences remain for some cases. Larger differences between the RVT and TS results occur for sites with smaller natural frequencies, for earthquakes of smaller magnitude, and for sites with larger bedrock shear-wave velocities. Accounting for the increase in duration due to site response in the RVT analysis minimizes the differences between RVT and TS analysis. Recommendations are provided regarding the cases where RVT provides site amplification reasonably similar to TS analysis.

Description: In this study, the strong-motion recordings collected by a vertical array of borehole sensors and a network of accelerometers installed in a nearby building (distance between borehole and building ~10 m) are innovatively jointly analyzed through wavefield-deconvolution analysis. The analysis shows complicated patterns in the deconvolved wavefield of the borehole sensors that are interpreted by taking advantage of synthetic seismograms generated considering vertically propagating plane waves in the soil and building. Using a constrained deconvolution approach, we show that it is possible to separate the different components of the wavefield and, in particular, to retrieve the input ground motion and the wavefield radiated back by the building at different levels in the borehole, without a priori information about the attenuation structure (and velocity) of the building and soil. This therefore allows the energy radiated back by the structure at different depth to be estimated, which, in the case of the bottom of the borehole (at –145 m), is of the order of 10% of the energy of the input wavefield in the 1–10 Hz frequency band.

Description: Earthquake ruptures comprise spatially varying slip on the fault surface, where slip represents the displacement discontinuity between the two sides of the rupture plane. In this study, we analyze the probability distribution of coseismic slip, which provides important information to better understand earthquake source physics. Although the probability distribution of slip is crucial for generating realistic rupture scenarios for simulation-based seismic and tsunami-hazard analysis, the statistical properties of earthquake slip have received limited attention so far. Here, we use the online database of earthquake source models (SRCMOD) to show that the probability distribution of slip follows the truncated exponential law. This law agrees with rupture-specific physical constraints limiting the maximum possible slip on the fault, similar to physical constraints on maximum earthquake magnitudes. We show the parameters of the best-fitting truncated exponential distribution scale with average coseismic slip. This scaling property reflects the control of the underlying stress distribution and fault strength on the rupture dimensions, which determines the average slip. Thus, the scale-dependent behavior of slip heterogeneity is captured by the probability distribution of slip. We conclude that the truncated exponential law accurately quantifies coseismic slip distribution and therefore allows for more realistic modeling of rupture scenarios. Online Material: Figures showing scaling of slip area with seismic moment and Q – Q plots and tables listing earthquakes, rupture models, and fits of various distributions to the empirical probability distribution.

Description: Confidence in scientific models accumulates by continuously validating the model’s predictions by observations. We compared the seismic-hazard forecasts of the four published versions of the U.S. Geological Survey National Seismic Hazard Maps with observed ground motions. A large dataset is necessary for a statistically meaningful comparison, and so our comparison was based on an aggregated approach such that the observations and the forecast in a region (California, and the central and eastern United States [CEUS]) were combined and compared as a whole. We used instrumental records in California and macroseismic intensity in the CEUS since 2000 as the observation, which was largely prospective to the hazard maps. We verified that the observed seismic hazard based on macroseismic intensity was consistent with that based on instrumental records, making model evaluation in the CEUS, for which instrumental records were almost nonexistent, viable. The observed hazard was found to be generally consistent with the forecasted one for peak ground acceleration (PGA) in California and for both PGA and spectral acceleration at 1 s (SA1) in the CEUS. Forecasted hazard for SA1 for California appeared to be conservative. Recent versions of the hazard map were in better agreement with observations in California. Small earthquakes, as expected, were found to have insignificant impact on SA1. Induced earthquakes in the CEUS have increased the observed seismic hazard but did not invalidate the hazard model as a whole. We examined the resolving power of the test by computing its statistical power.

Description: As opposed to the conventional 2D (circular/elliptical crack) and 1D (linear crack) models for earthquake rupture, which are, respectively, for small-to-large earthquakes and mega-earthquakes, Vere-Jones’ branching crack model describes the extreme case when the entire rupture process is completely controlled by randomness. This article discusses the similar features between the conventional source models and Vere-Jones’ branching crack model, which include (a) the magnitude–frequency relation, (b) the source time function, and (c) the rupture duration–seismic moment relation. We proved that the Gutenberg–Richter magnitude–frequency relation holds as an asymptote for more general cases of branching processes. The branching crack model shows that the variance of observed rupture durations is relatively larger for small magnitudes and gives a scaling relation of T M 1/2 between the rupture duration T and the seismic moment M of an earthquake. Moreover, the stochastic property of the branching process explains why the earthquake magnitude cannot be determined until the entire source process is completed. The results in this article imply that the randomness caused by many unknown factors in the complex environments of earthquake sources cannot be ignored, and it can be effectively described by Vere-Jones’ branching crack model. We conclude that the earthquake rupture is at least an intermediate process between the conventional deterministic model and the stochastic branching crack model if its mechanism is not completely controlled by randomness, as described by the latter.

Description: We present a strategy for the region-specific assessment, adjustment, and weighting of ground-motion prediction models, with application to the 2015 Swiss national seismic-hazard maps. The models are provided within a logic-tree framework adopted for the probabilistic seismic-hazard analysis (PSHA). Through this framework, we consider both aleatory and epistemic uncertainties in ground-motion prediction in Switzerland, a region of low-to-moderate seismicity and consequently data poor in terms of strong-motion records. We use both empirical models developed using global strong-motion data and stochastic simulation models calibrated to local seismicity, characteristic wave-propagation effects, and site conditions. The empirical models were adjusted to account for (a) the selected hazard reference rock velocity model (using V S - 0 adjustments) and (b) the median instrumental ground-motion data at low magnitudes. The use of a carefully calibrated simulation model and V S - 0 adjusted empirical ground-motion prediction equations allowed us to precisely define the reference-rock profile, upon which subsequent analyses, such as microzonation and site-specific hazard, can be applied without uncertainty related to the reference condition. We implemented partially nonergodic aleatory uncertainties in ground-motion prediction through the single-station sigma approach. This strategy, complemented with the known reference rock condition, leads to significant reductions in the contribution of uncertainty in ground-motion characterization to PSHA in Switzerland. However, the application of the methodological framework outlined herein extends to any region, particularly those of low-to-moderate seismicity. Online Material: Tables of adjustment factors to convert selected ground-motion prediction equations (GMPEs) to the Swiss rock reference and figures showing trellis plots of all adjusted GMPEs with uncertainty estimates.

Description: I used seismic waveforms recorded within 2 km from the epicenter of the first four Source Physics Experiments (SPE) explosions to invert for the moment tensor spectra of these explosions. I employed a 1D Earth model for Green’s function calculations. The model was developed from P - and Rg -wave travel times and amplitudes. I selected data for the inversion based on the criterion that they had consistent travel times and amplitude behavior as those predicted by the 1D model. Because of limited azimuthal coverage of the sources and the mostly vertical-component-only nature of the dataset, only long-period, volumetric components of the moment tensor spectra were well constrained. The source spectra, particularly their long-period levels and corner frequencies, could not be fit by traditional explosion source models. To achieve a better fit, I used a model with parameters derived from regressing observed values against source yield and depth. These values were calculated from measured source moments and corner frequencies. Although the number of data points used in the regression is small, the approach suggests a potential way to develop a source model for chemical explosions when more data with wider coverage of yield, depth of burial, and material property are collected.

Description: This study presents a global sensitivity analysis (SA) of the near-fault probabilistic seismic-hazard analysis (PSHA) model. The influence of the model inputs on the computed PSHA results was investigated using the information-theoretic SA approach. This process is utilized at three different sites in the city of Tehran, the capital of Iran, to identify the most important uncertain inputs by using an entropy-based sensitivity index as a measure of importance. The analysis showed that the degree of sensitivity of the input variables depends on the site of interest, return period, and structural periods. Using the results obtained, the ground-motion prediction equations, the minimum magnitude, and b -value variables most influence the uncertainty in the hazard estimation. Moreover, the maximum magnitude and the variables that were used to model the near-fault directivity have a significant contribution at near-fault sites.

Description: Results of probabilistic seismic hazard analysis (PSHA) depend on the soil conditions of the site investigated. Consequently, it is generally expected that disaggregation, usually employed to gather further information about hazard levels of interest, changes with the soil class. This short note discusses the relationship between hazard curves and disaggregations computed for different soil conditions at the same site. In particular, it is analytically proven that there are cases, depending on the structure of the ground-motion prediction equations employed, in which disaggregations for different soil conditions are necessarily invariant. It is also demonstrated that, in these situations, hazard curves for different soil conditions can be immediately obtained from a curve developed for a reference soil class. The analytical proofs derived do not require any further testing or validation; nevertheless, the results are illustrated via simple case studies to show how they may imply applicative advantages both in the cases of single-model and logic tree PSHA.

Description: Liquefaction features and the geologic environment in which they formed were carefully studied at two sites near Lincoln in southwest Christchurch. We undertook geomorphic mapping, excavated trenches, and obtained hand cores in areas with surficial evidence for liquefaction and areas where no surficial evidence for liquefaction was present at two sites (Hardwick and Marchand). The liquefaction features identified include (1) sand blows (singular and aligned along linear fissures), (2) blisters or injections of subhorizontal dikes into the topsoil, (3) dikes related to the blows and blisters, and (4) a collapse structure. The spatial distribution of these surface liquefaction features correlates strongly with the ridges of scroll bars in meander settings. In addition, we discovered paleoliquefaction features, including several dikes and a sand blow, in excavations at the sites of modern liquefaction. The paleoliquefaction event at the Hardwick site is dated at A.D. 908–1336 , and the one at the Marchand site is dated at A.D. 1017–1840 (95% confidence intervals of probability density functions obtained by Bayesian analysis). If both events are the same, given proximity of the sites, the time of the event is A.D. 1019–1337. If they are not, the one at the Marchand site could have been much younger. Taking into account a preliminary liquefaction-triggering threshold of equivalent peak ground acceleration for an M w  7.5 event (PGA 7.5 ) of 0.07 g , existing magnitude-bounded relations for paleoliquefaction, and the timing of the paleoearthquakes and the potential PGA 7.5 estimated for regional faults, we propose that the Porters Pass fault, Alpine fault, or the subduction zone faults are the most likely sources that could have triggered liquefaction at the study sites. There are other nearby regional faults that may have been the source, but there is no paleoseismic data with which to make the temporal link. Online Material: Figures showing areas of liquefaction, trench logs, information on dike and sand-blow parameters, dike azimuths, core logs, radiocarbon samples, and OxCal analysis, and tables detailing units exposed in the trenches and stereonets.

Description: The 2004 M w  6 Parkfield, California, earthquake was preceded by a 4-year period of anomalously high seismicity adjacent to, but not on, the San Andreas fault. The rate of small events ( M w 〈3) at distances between 1.5 and 20 km from the fault plane and at depths 〉8 km, increased from 6 events per year prior to 2000 to 20 events per year between the 2000 and the 2004 earthquake. This increase in seismicity coincided with an increase in the rate of nonvolcanic tremor, which, if tremor is indicative of creep on the fault plane, suggests that creep may have driven the enhanced seismicity. Coulomb stress-transfer calculations predict the observed spatial pattern of the seismicity, and thus support a causal relation between creep at the base of the fault zone and off-fault seismicity. In particular, an observed southeast-striking lineation of enhanced seismicity is shown to be a direct consequence of a deepening boundary between the crust and mantle southeast of Parkfield, as evidenced by a deepening of the tremor and low-frequency earthquakes. Other evidence for a causal link between deep creep and off-fault seismicity is the observation that off-fault seismicity before and after the 2004 earthquake occurred in the same location. This is expected if the foreshocks are driven by an episode of deep creep and the aftershocks are driven by afterslip, both occurring on the same deep extension of the fault plane.

Description: We evaluate the performance of earthquake early warning algorithm ElarmS-2 (earthquake alarm system v. 2) in the Pacific Northwest. Real-time and prerecorded seismic data from Oregon, California, and Washington in the United States and British Columbia in Canada are used. The earthquakes tested range up to moment magnitude 7.2, the limit for which the ElarmS-2 magnitude method is accurate. ElarmS-2 reliably detects catalog magnitude 3 and larger earthquakes within the network, but the cut-off magnitude for accurate event recognition is higher for events offshore and on the edges of the network. We have made several adjustments that make the ElarmS-2 algorithm less likely to falsely report multiple alerts for earthquakes. Replaying of past earthquakes shows that the new settings improve the algorithm’s behavior for edge cases while not degrading previously well-constrained solutions within the dense part of the network. We expect few false alerts, none that would predict significant shaking anywhere in our region. Even though ElarmS-2 assumes a fixed earthquake depth, the epicenter and magnitude estimates are accurate enough to provide good predictions of shaking intensities. Online Material: Tables listing parameters of 31 calibration earthquakes, ElarmS-2 real-time detections, and comparison of ElarmS-2 performance for calibration events before and after adjusting configuration.

Description: A 1D normal moveout (NMO)-corrected and stacked pseudoprofiling method was applied to analyze the characteristic features shown on primary P - and S -wave coda and on Sp waveforms from local microearthquakes in an attempt to image prominent reflectors and to resolve shallow crustal velocity structure (~5 km) in the upper Mississippi embayment. Acoustic well log data were used to constrain the P -wave velocity in the upper 5 km. Events at close distances and with clear P and S arrivals were selected to ensure reliable NMO correction for reflections and transmissions. The observed reflections and transmissions are important controlling factors on modeling waveforms. We analyzed local earthquake data recorded at all broadband and one short-period station of the Cooperative New Madrid Seismic Network. Despite polarity differences among P , S , and Sp waveforms, consistent reflectors in the sedimentary section can be imaged across the three wave types. Correlation with a basement-penetrating well indicates that reflectors at the base of the Upper Cretaceous–Holocene Mississippi Embayment Supergroup, the base of the Cambrian–Ordovician Knox Group, and the high-velocity lower Upper Cambrian Bonneterre Formation are shown in pseudoprofiles among stations in the upper Mississippi embayment. Our study finds that a one-layer homogeneous velocity model of sediments in the ranges of 1.95–2.42 km/s for V P and 0.60–0.73 km/s for V S overlying a half-space of Paleozoic rocks with velocities in the ranges of 6.0–6.2 km/s for V P and 3.26–3.6 km/s for V S can represent shallow crustal structure in the upper Mississippi embayment. Differential times of P – PpPhp and S – SsShs appear linearly proportional to sediment thicknesses, which best fits a one-layer sediment structure with average V P 2.042±0.041 km/s and V S 0.709±0.051 km/s, in the least-squares sense predicted by the wave propagation effects. Online Material: Figures illustrating seismograms, process procedure, imaged reflectors, and resolved velocity structure for six broadband stations and one short-period station.

Description: In the present study, the scattering and intrinsic attenuation are separated using the S -wave attenuation ( Q β ) and coda-wave attenuation ( Q c ) employing the Wennerberg (1993) method, and the frequency-dependent Q s and Q i relations have been developed for the region. The Q i and Q s show the frequency-dependent character in the frequency range 1.5–24 Hz. The average scattering and intrinsic relationships are obtained for the region as Q s =(31±1) f 1.04±0.02 , Q s =(48±1) f 1.05±0.02 , and Q s =(61±1) f 1.05±0.02 and as Q i =(68±1) f 0.95±0.06 , Q i =(134±1) f 1.01±0.05 , and Q i =(167±1) f 0.96±0.03 for lapse time windows of 30, 40, and 50 s, respectively. The quality factor for the P wave ( Q α ) and the S wave ( Q β ) are estimated using the extended coda-normalization method of Yoshimoto et al. (1993) . The frequency dependence Q α and Q β relationships are obtained as Q α =(25±1) f (1.24±0.04) for the P wave and Q β =(58±1) f (1.16±0.04) for the S wave. The quality factor for the coda wave ( Q c ) is estimated using the single backscattering model of Aki and Chouet (1975) . The comparison of Q β and Q c with Q i and Q s shows that both Q i and Q s are lower than the Q β , as well as Q c , at 30 s lapse time. As the lapse time increases, both Q i and Q s increase in such a manner that Q c will increase because it contains the effects of both. This agrees with the theoretical as well as the laboratory measurements. Also Q c is higher than Q β ; this supports the model given by Zeng et al. (1991) , which predicts that the combination of Q i and Q s should be such that Q c is more than Q β .

Description: Knowledge of the typically complicated near-surface structure on volcanoes is critical for determining accurate seismic-event locations and seismic source mechanisms associated with precursory and eruptive activity. To generate a near-surface velocity model for the active cone of Pacaya volcano, Guatemala, we recorded seismic tremor and ambient noise with a small-aperture array of 11 short-period seismometers in January 2011. The diffuse wavefield was investigated using the spatial autocorrelation (SPAC) method, and we computed Rayleigh and Love dispersion curves at the array location. The phase velocities for Rayleigh waves range from 1000 m/s at 2 Hz to 230 m/s at 10 Hz; those for Love waves range from 600 to 250 m/s over the same frequency band. Such low velocities are consistent with the presence of unconsolidated tephra on the surface of the volcano interspersed with lava flows. Assuming they represent the fundamental modes of Rayleigh and Love waves, we inverted the dispersion curves to produce a shear-wave velocity model of the upper 500 m beneath the array. Online Material: S -wave velocity models obtained from inversion, and Love- and Rayleigh-wave dispersion curves.

Description: We introduce a nondiagonal seismic denoising method based on the continuous wavelet transform with hybrid block thresholding (BT). Parameters for the BT step are adaptively adjusted to the inferred signal property by minimizing the unbiased risk estimate of Stein (1980) . The efficiency of the denoising for seismic data has been improved by adapting the wavelet thresholding and adding a preprocessing step based on a higher-order statistical analysis and a postprocessing step based on Wiener filtering. Application of the proposed method on synthetic and real seismic data shows the effectiveness of the method for denoising and improving the signal-to-noise ratio of local microseismic, regional, and ocean bottom seismic data.

Description: In 2001, a rare swarm of small, shallow earthquakes beneath the city of Spokane, Washington, caused ground shaking as well as audible booms over a five-month period. Subsequent Interferometric Synthetic Aperture Radar (InSAR) data analysis revealed an area of surface uplift in the vicinity of the earthquake swarm. To investigate the potential faults that may have caused both the earthquakes and the topographic uplift, we collected ~3 km of high-resolution seismic-reflection profiles to image the upper-source region of the swarm. The two profiles reveal a complex deformational pattern within Quaternary alluvial, fluvial, and flood deposits, underlain by Tertiary basalts and basin sediments. At least 100 m of arching on a basalt surface in the upper 500 m is interpreted from both the seismic profiles and magnetic modeling. Two west-dipping faults deform Quaternary sediments and project to the surface near the location of the Spokane fault defined from modeling of the InSAR data.

Description: Using the single backscattering method, coda quality factor functions through coda window lengths of 20, 30, 40, 50, and 60 s have been estimated for the New Madrid seismic zone (NMSZ). Furthermore, geometrical spreading functions for distances less than 60 km have been determined in this region at different center frequencies exploiting the coda normalization method. A total of 284 triaxial seismograms with good signal-to-noise ratios (SNR〉5) from broadband stations located in the NMSZ were used. The database consisted of records from 57 local earthquakes with moment magnitudes of 2.6–4.1, and hypocentral distances less than 200 km. Q -factor values were evaluated at five frequency bands with central frequencies of 1.5, 3, 6, 12, and 24 Hz. Vertical components were utilized to estimate vertical coda Q -factor values. Horizontal coda Q -factor values were determined using the average amount of the Q -factor values estimated from two orthogonal horizontal components. The coda Q -factor increases with increasing of the coda window length implying that with increasing the depth, the coda Q -factor increases. The intermediate values of the Q -factor and intermediate values of the frequency dependency indicate that the Earth’s crust and upper mantle beneath the entire NMSZ is tectonically a moderate region with a moderate to relatively high degree of heterogeneities. The geometrical spreading factors of S -wave amplitudes are frequency dependent and determined to be –0.761, –0.991, –1.271, –1.182, and –1.066 for center frequencies of 1.5, 3, 6, 12, and 24 Hz, respectively, at hypocentral distances of 10–60 km. The geometrical spreading factors for lower frequencies are not recommended to be used due to the greater impact of the radiation pattern and directivity effect on low frequencies, as well as the greater sensitivity of band-pass-filtered seismograms of small earthquakes to the noise in low frequencies.

Description: We analyzed 14 local earthquakes of the Mexico basin (2.3≤ M w ≤3.8), recorded on hill sites at local distances (8.0≤ R ≤60.5 km), to study the spectral attenuation of seismic waves, spectral decay parameter kappa , quality factor Q , source spectra, and Brune stress drop. We found an average 0 -value of 0.0457 s in hill sites, which is similar to values reported in other regions. Assuming a 1/ R geometrical spreading, we obtain a quality factor given by Q ( f )=72 f 0.83 . Source spectra of all studied events are in good agreement with the 2 model. From the synthetic modeling of ground motions at local distances, we explain an anomalous behavior of the corner frequency versus seismic moment and also explain the relatively low values observed for stress drop (5 MPa). The resulting high spectral attenuation values obtained may be responsible for the low acceleration values of ground motions observed for crustal earthquakes occurring inside and near to the Mexico basin.

Description: The distribution of damage due to recent earthquakes has shown that the effects of shallow geological structures on the level of ground shaking represent an important factor in engineering seismology. Whereas many previous studies have estimated site amplification factors in the frequency domain, their application to the real-time modeling of ground motion is not yet fully established. In this article, a method for the real-time correction of frequency-dependent site-response factors is proposed, which accounts not only for the modulus, but also for the changes in the signal phase related to local site conditions. The transformation of the complex standard spectral ratios to a causal recursive filter in the time domain allows for the forecasting of the waveforms for soft-soil sites almost in real time when the signal is recorded earlier at a reference site. When considering travel-time differences of the various seismic phases between the hypocenter and the studied sites, the level of ground motion at soft-soil sites with respect to arrival time, energy, duration, and frequency content can be well constrained, even in cases of a high spatial variability of the amplification patterns.

Description: Seismic hazard in terms of mean peak ground acceleration (PGA) and spectral acceleration (SA) values has been computed for Egypt using both historical and instrumental earthquake data. For this purpose, an updated earthquake catalog, spanning the time period from 2200 B.C. to 2013, has been compiled for Egypt as well as its surrounding regions and is prepared to be used in a new probabilistic seismic-hazard assessment of Egypt. The earthquakes sizes were unified in terms of the moment magnitude scale. A new seismic source model for the seismic activity in and around Egypt, consisting of a total of 88 seismic zones (for shallow- and intermediate-depth seismicity), was considered in this new assessment. The seismicity parameters have been specifically computed for 35 seismic sources covering the Egyptian territory and the Eastern Mediterranean region. A logic-tree design was set up to consider the epistemic uncertainty in the Gutenberg–Richter b -value, maximum possible magnitude ( M max ), and the selected ground-motion prediction equations. Seismic-hazard computations for rock-site conditions with 10% and 5% probability of exceedance in 50 years were carried out. In addition, uniform hazard spectra for twelve, among the most important and populated cities in Egypt, are computed and compared with the most recent Egyptian building code values. It is interesting to highlight that the maximum hazard values are observed at the Gulf of Aqaba region, specifically around the epicentral location of the biggest Egyptian recorded earthquake of 22 November 1995 ( M w  7.2) Aqaba earthquake. The obtained seismic-hazard values for Nuweiba city (located in this region) for mean PGA and SA (0.1 s) are 0.29 g and 0.74 g , respectively, for a return period of 475 years.

Description: Numerical simulations of complex earthquake cycles are conducted using a model with two patches (asperities) on a fault, where friction obeys a rate-and-state-dependent law. The patches are represented by regions of steady-state velocity-weakening friction and are in contact with each other or are separated by a region of steady-state velocity-strengthening friction. Simulated earthquake cycles are examined by changing the characteristic slip distance of friction in one patch, while that in the other patch is maintained at a constant. As the characteristic slip distance in a patch increases, the slip at the patch tends to be aseismic and rupture tends to be delayed, as compared to rupture at the other patch, or arrested due to an increase in fracture energy. As a result, the slip pattern changes in a complicated manner with the change of the parameter. A complex multiperiodic or aperiodic slip pattern occurs in the simulation, and this pattern tends to occur near the boundaries between regions of different slip behavior characteristics, such as the boundary between seismic and aseismic slip in the patch with a larger characteristic slip distance. Iteration maps of the recurrence intervals of simulated earthquakes for an aperiodic sequence are sometimes expressed by simple curves, suggesting that the simulated earthquake cycles exhibit deterministic chaos. In the two-patch models of the present study, an aperiodic slip pattern is observed for narrower parameter ranges than in a model of a two-degree-of-freedom spring-block system, which is usually regarded as a simplified model of a fault with two patches. Online Material: Simulated histories of moment release rate and recurrence interval of simulated slip events in the two patches and seismic coupling coefficients.

Description: Faults may rupture across several segments of plate boundaries, generating earthquakes of M  9 class. Along the Pacific coast of Mexico, a rupture of 450 km on 28 March 1787 generated an M w  8.6 earthquake. Intensity values ( I ) of VII were reported at the Atlantic coast, and the maximum was XI in Oaxaca. Here, we estimate the number of casualties if an M  9 rupture were to occur at present. We verified that our software tool, QLARM, with its database, estimates intensities and fatalities approximately correctly for historic earthquakes along the Pacific coast. Our test set consists of 10 earthquakes ( M w  7.3–8.6) that caused between 0 and ~10,000 fatalities between 1787 and 2003. Requirements for a satisfactory match are that the maximum I agrees within 0.5 units, the extent of the I =VII area agrees approximately, and the fatality count differs by not more than a factor of 2 or by 200 fatalities, whichever is larger. Results for Mexico, without the special case of Mexico City, suggest that an M  9 earthquake would cause approximately 27,000 fatalities and 120,000 injuries. Applying amplification factors to the ground motion in 11 of 15 districts, we estimate that, in an M  9 along the Pacific coast, 100,000 people may perish and 480,000 may be injured in Mexico City. The number of people in settlements with fewer than 20,000 inhabitants exposed to large I exceed the exposed population in larger cities by factors of 3–10. The estimated mortality rate in rural areas is several times higher than in major population centers.

Description: Liquefaction of fully saturated sediments subjected to earthquake motion is often defined by the condition when effective stress reaches zero. On the other hand, the gradient of excess pore-water pressure represents the net local surface force, which plays a crucial mechanical role for liquefaction. Herein, we consider two definitions of liquefaction, which yield different liquefaction initiation times and depths. Two hypothetical cases of liquefaction, earthquake-induced and tsunami-induced, are given to highlight the differences in the definitions of liquefaction. The results from the hypothetical cases show that the effective stress definition of liquefaction is a special case of the pore-water pressure gradient definition of liquefaction.

Description: When a major earthquake strikes, the resulting devastation can be compounded or even exceeded by the subsequent cascade of triggered seismicity. As the Nepalese recover from the 25 April 2015 shock, knowledge of what comes next is essential. We calculate the redistribution of crustal stresses and implied earthquake probabilities for different periods, from daily to 30 years into the future. An initial forecast was completed before an M  7.3 earthquake struck on 12 May 2015 that enables a preliminary assessment; postforecast seismicity has so far occurred within a zone of fivefold probability gain. Evaluation of the forecast performance, using two months of seismic data, reveals that stress-based approaches present improved skill in higher-magnitude triggered seismicity. Our results suggest that considering the total stress field, rather than only the coseismic one, improves the spatial performance of the model based on the estimation of a wide range of potential triggered faults following a mainshock.

Description: We employ a network-based method to map the spatiotemporal variations of the magnitude of completeness ( M c ) in the Composite Alberta Seismicity Catalog (CASC; see Data and Resources ) from 1985 to 2015 across a grid of sites. The underlying principle is that we expect events to be located and cataloged if they are detected on four or more seismic stations. Seven M c maps are created to represent spatial variations of M c in time periods: 1985–1989, 1990–1999, 2000–2006, 2007–2009, 2010, 2011–2013, and 2014–2015. By counting the annual number of events above M c since 1985, and assuming a Gutenberg–Richter b -value of 1.0, we calculate the equivalent number of M ≥3 earthquakes in eight relatively active grid cells. In several areas, there is clear evidence of changes of seismic rate over time. Overall, seismicity in Alberta is highly clustered in both space and time.

Description: Seismic sensor orientation is one of the most critical parameters for modern three-component seismological observation. However, this parameter is easily subject to error imposed by strong magnetic anomalies near the station or by human error in declination calibration. It is therefore very important to inspect and correct for sensor misorientation before utilizing three-component waveform data. In this study, we measured the epoch-dependent sensor misorientation for our temporary seismic array (NorthEast China Seismic Array to Investigate Deep Subduction, or NECsaids) by analyzing P -wave particle motions. We applied principal component analysis and the minimizing transverse energy method to study earthquakes with epicentral distance between 5° and 90° to estimate the sensor misorientation. Our results show high consistency with the direct gyrocompass measurements, with a correlation coefficient of 0.95. Our statistical analysis suggests that we can estimate robust sensor misorientation utilizing 10 earthquakes with high signal-to-noise ratio records and highly linear P -wave polarizations. We also find that the influence of anisotropy or a dipping interface produces a periodical pattern with back azimuth and is relatively small for our misorientation estimation. By analyzing the amplitude change of synthetic seismograms due to misorientation and taking into account the influence of anisotropy and dipping interfaces, as well as the measurement errors, we expect engineers to be able to orient seismic sensors with error smaller than 3°.

Description: We use the new global database of source time functions (STFs) and focal mechanisms proposed by Vallée (2013) using the automatic SCARDEC method ( Vallée et al. , 2011 ) to constrain earthquake rupture duration and variability. This database has the advantage of being very consistent since all the events with moment magnitudes M w 〉5.8 that have occurred during the last 20 years were reanalyzed with the same method and the same station configuration. We analyze 1754 shallow earthquakes (depth〈35 km) and use high-quality criteria for the STFs, which result in the selection of 660 events. Among these, 313 occurred on the subduction interface (SUB events) and 347 outside (NOT-SUB events). We obtain that for a given magnitude, STF duration is log normally distributed and that STFs are longer for SUB than NOT-SUB events. We then estimate the stress drop using a proxy for the rupture process duration obtained from the measurement of the maximum amplitude of the STF. The resulting stress drop is independent of magnitude and is about 2.5 times smaller for the subduction events compared with the other events. Assuming a constant rupture velocity and source model, the resulting standard deviation of the stress drop is 1.13 for the total dataset (natural log), and about 1 for separate datasets. These values are significantly lower than the ones generally obtained from corner-frequency analyses with global databases (~1.5 for Allmann and Shearer, 2009 ) and are closer to the values inferred from strong-motion measurements (~0.5 as reported by Cotton et al. , 2013 ). This indicates that the epistemic variability is reduced by the use of STF properties, which allows us to better approach the natural variability of the source process, related to stress-drop variability and/or variation in the rupture velocity.

Description: We present the software package hybridMT which allows performing seismic moment tensor inversion and refinement, optimized for earthquake data recorded by regional-to-local seismic networks as well as for acoustic emission activity. The provided software package is designed predominantly for use in MATLAB (see Data and Resources )/shell environments. The algorithm uses first P -wave amplitudes to invert for unconstrained full, deviatoric, and double-couple constrained moment tensors. Uncertainty assessment is performed by bootstrap resampling. The moment tensor inversion may be performed directly in the shell environment (by a dedicated command-line tool) or conveniently through the MATLAB interface (m-functions). In addition to moment tensor inversion, we also provide the MATLAB implementation of the hybrid moment tensor technique. This methodology increases the quality of calculated seismic moment tensors from events forming a spatial cluster by assessing and correcting for poorly known path and site effects. We tested hybridMT on synthetic datasets, acoustic emission data recorded during laboratory rock deformation experiments, and induced seismicity data from a geothermal reservoir. The package is supplemented with extensive documentation, tutorials, and a dedicated website. HybridMT is freely available and distributed under General Public License.

Description: Aftershock sequences following very large earthquakes present enormous challenges to near-real-time generation of seismic bulletins. The increase in analyst resources needed to relocate an inflated number of events is compounded by failures of phase-association algorithms and a significant deterioration in the quality of underlying, fully automatic event bulletins. Current processing pipelines were designed a generation ago, and, due to computational limitations of the time, are usually limited to single passes over the raw data. With current processing capability, multiple passes over the data are feasible. Processing the raw data at each station currently generates parametric data streams that are then scanned by a phase-association algorithm to form event hypotheses. We consider the scenario in which a large earthquake has occurred and propose to define a region of likely aftershock activity in which events are detected and accurately located, using a separate specially targeted semiautomatic process. This effort may focus on so-called pattern detectors, but here we demonstrate a more general grid-search algorithm that may cover wider source regions without requiring waveform similarity. Given many well-located aftershocks within our source region, we may remove all associated phases from the original detection lists prior to a new iteration of the phase-association algorithm. We provide a proof-of-concept example for the 2015 Gorkha sequence, Nepal, recorded on seismic arrays of the International Monitoring System. Even with very conservative conditions for defining event hypotheses within the aftershock source region, we can automatically remove about half of the original detections that could have been generated by Nepal earthquakes and reduce the likelihood of false associations and spurious event hypotheses. Further reductions in the number of detections in the parametric data streams are likely, using correlation and subspace detectors and/or empirical matched field processing.

Description: This article describes the Engineering Strong-Motion Database (ESM), developed in the framework of the European project Network of European Research Infrastructures for Earthquake Risk Assessment and Mitigation (NERA, see Data and Resources ). ESM is specifically designed to provide end users only with quality-checked, uniformly processed strong-motion data and relevant parameters and has done so since 1969 in the Euro-Mediterranean region. The database was designed for a large variety of stakeholders (expert seismologists, earthquake engineers, students, and professionals) with a user-friendly and straightforward web interface. Users can access earthquake and station information and download waveforms of events with magnitude≥4.0 (unprocessed and processed acceleration, velocity, and displacement, and acceleration and displacement response spectra at 5% damping). Specific tools are also available to users to process strong-motion data and select ground-motion suites for code-based seismic structural analyses.

Description: A critical component in the interpretation of earthquake ground motions is the role that site effects play. In eastern Canada, the sediment layers which overlie glaciated bedrock produce strong and highly variable site responses. We use horizontal-to-vertical (H/V) response spectral ratios as the indicator variable by which to characterize the salient characteristics of site response. We show that site response can be modeled using two key descriptive variables that are readily obtainable: (1) peak frequency ( f peak ), as determined from H/V or sediment depth; and (2) overall sediment type (or stiffness). We use these variables to create a preliminary model of site amplification that can be used in the development of ground-motion prediction equations (GMPEs) and in regional-scale ShakeMap-type applications. The key to the site characterization is the relationship between f peak and sediment thickness (depth-to-bedrock), which we derive using H/V data from earthquakes in the region, combined with compiled geophysical logs and a digital sediment thickness map from the Ontario Geological Survey (OGS). The OGS map also provides information on surficial sediment type, which is correlated with peak amplitudes ( A peak ) of response. H/V spectral shapes may be associated with four main site categories, which in decreasing order of stiffness are: bedrock, till, sand/clay, and organic sediment/fill. The peak amplitudes of response are generally shown to increase as stiffness decreases, at least for the weak motions that are the focus of this study. We model site response by defining a generic site amplification curve, which is dependent only on f peak and site category. These site amplification curves can be applied in the development of regional GMPEs, and in the construction of near-real-time ShakeMaps.

Description: The aim of the current study is to explore the effectiveness of using inquiry instruction to support high school students’ learning of seismology. A total of 191 Taiwanese high school students were recruited and assigned to the guided-inquiry condition or the structured-inquiry condition. Students’ learning outcomes (i.e., basic knowledge of seismology, applications of basic knowledge, and attitudes toward seismology) were assessed. The results revealed that the guided-inquiry group outperformed the structured-inquiry group in the application of basic knowledge. In contrast, the structured-inquiry group had a better understanding of basic seismological information. Both groups’ attitudes toward seismology were improved after the inquiry activities. The findings suggest that both guided and structured inquiries are effective in enhancing students’ learning of seismology, albeit in different ways. Accordingly, teachers should be flexible in using different approaches to inquiry activity to maximize students’ learning.

Description: We present the European Rapid Raw Strong-Motion database (RRSM), a new Europe-wide system that provides parameterized earthquake ground-motion information, as well as access to waveform data, within minutes of the occurrence of any earthquake with M ≥3.5 occurring in the European–Mediterranean region. The RRSM is different from traditional platforms for disseminating earthquake strong-motion data in Europe, which focus on providing reviewed, processed strong-motion parameters, typically with significant delays. The RRSM provides rapid open access to raw waveform data and metadata and does not rely on manual waveform processing. The RRSM targets seismologists and strong-motion data analysts, earthquake and geotechnical engineers, international earthquake response agencies, and the educated general public. The database is accessible online (see Data and Resources ). Users can query earthquake information, peak ground-motion parameters, and select and download earthquake waveforms. The RRSM database is populated using the waveform processing module scwfparam , which is integrated in SeisComP3. Processing is triggered using earthquake parameters provided by the European–Mediterranean Seismological Center and uses all significant waveform data that are available in the European Integrated waveform Data Archive (EIDA). EIDA consists of broadband and strong-motion data from across Europe, and the majority of these data are available in near real time. All relevant, on-scale open EIDA data are processed for the RRSM. As the EIDA community is continually growing, the already significant number of strong-motion stations is also increasing and the importance of the RRSM database is expected to grow further in time. Real-time RRSM processing started in September 2014, whereas offline reprocessing was carried out for all M 4.5+ events that occurred since January 2005.