ALBERT

Description: We present a database of field data for active faults in the central Apennines, Italy including trace, fault and master fault locations with activity and location certainties, and slip-rate, slip-vector and surface geometry data. As advances occur in our capability to create more detailed fault-based hazard models, depending on the availability of primary data and observations, it is desirable that such data can be organized in a way that is easily understood and incorporated into present and future models. The database structure presented herein aims to assist this process. We recommend stating what observations have led to different location and activity certainty and presenting slip-rate data with point location coordinates of where the data were collected with the time periods over which they were calculated. Such data reporting allows more complete uncertainty analyses in hazard and risk modelling. The data and maps are available as kmz, kml, and geopackage files with the data presented in spreadsheet files and the map coordinates as txt files.

Description: In 2006 we published an earthquake hazard model called LASSCI (LAyered Seismogenic Source model in central Italy). In October 2008 we began to update the model for use in 5- and 10-year forecasts. The LASSCI-2006 model is supported by good fault-based definitions of seismogenic sources and simple physically motivated models of earthquake occurrence; the LASSCI-2009 model has been improved by revision of the error propagation assumptions and increased accuracy of the earthquake probabilities. The 6 April 2009 earthquake that struck L'Aquila occurred on the model fault having the highest probability of occurrence in the 2009 revised LASSCI forecast: it is therefore consistent with our model assumptions. Furthermore, peak ground accelerations were in reasonable agreement with the values having 90% probability of not being exceeded in 50 yr. In the revised 2009 model, the aggregate probability of having a maximum-sized event in the next 5 yr on at least one of the neighboring sources (less than 25 km distance away) decreases in L'Aquila from 10% to 7% after the earthquake occurrence, but still remains a maximum there along the central Apennines. The LASSCI models 2006 and 2009, featuring characteristic fault sources and time dependence, seem to be suitable for guidance in reconstruction and seismic retrofit in the central Appenines.

Description: With the aim of estimating the rates of seismic moment and deformation in seismic zones of southern Italy, constraints on tectonic style and kinematics data from geophysical and geologic data were integrated with the traditional constraints from seismicity catalogues. Seismotectonic considerations indicate that the region can be divided into four broad crustal seismogenic volumes, of relatively homogeneous deformation: an extensional crustal volume in the western part of the Southern Apennines and three crustal volumes characterized by a transcurrent regime in the eastern area.For each crustal volume, the annual seismic moment release showing the rate of the deformation was estimated by integrating magnitude-frequency relations of historical earthquakes. The application of a Monte Carlo simulation systematically incorporated the uncertainties of the input parameters.The results show that the westernmost crustal volume is undergoing extension, with velocity of ∼1.2 mm/a (along a nearly NE-SW direction), whereas the easternmost volumes are undergoing transcurrent deformation, with an along-strike deformation axis oriented along a nearly E-W direction, with velocities of ∼1 mm/a, ∼1.2 mm/a and ∼0.1 mm/a, respectively for the northern, central and southern volumes.The errors affecting the estimate of the crustal deformation using the seismicity catalogues may be significant. The parameters with the largest contribution are the coefficients of the magnitude-moment relationship; the second and third contributors are the coefficients of the magnitude-frequency distribution and the maximum magnitude. Uncertainties in the geometrics and kinematics parameters have slight, minor effects. Furthermore, the effects of the crustal model (and the consequent earthquake association) are of the same order as the uncertainties of the parameters involved in the computation.These results agree with recent GPS data and geological slip rates in terms of direction and rate of deformation.

Description: Italy is one of the most seismically active countries in Europe. Moderate to strong earthquakes, with magnitudes of up to ~ 7, have been recorded on many of active faults in historical times. Currently, probabilistic seismic hazard assessments in Italy are mainly based on area source models, in which the seismicity is modelled on a number of seismotectonic zones and the occurrence of earthquakes is assumed to be uniform. However, in the last decade, efforts have increasingly been directed towards using fault sources in seismic hazard models to obtain more detailed and possibly more realistic patterns of ground motion. In our model, we used two categories of earthquake sources. The first involves active faults, and fault slip rates were used to quantify the seismic activity rate. We produced an inventory of all fault sources, with details on their geometric, kinematic and energetic properties. The parameters are used to compute the total seismic moment rate for each fault. We evaluated the magnitude-frequency distributions of each fault source using two models, a characteristic Gaussian model centred on the maximum magnitude and a Truncated Gutenberg-Richter model. The second earthquake source category involves distributed seismicity, and a fixed-radius smoothed approach and a historical catalogue were used to evaluate seismic activity. Under the assumption that deformation is concentrated along faults, we combined the earthquakes derived from the geometry and slip rates of active faults with the earthquakes from the spatially smoothed earthquake sources and assumed that the smoothed seismic activity in the vicinity of an active fault gradually decreases by a fault-size driven factor. We computed horizontal peak ground acceleration maps for return periods of 475 and 2,475 yr. Although the range and gross spatial distribution of the expected accelerations obtained here are comparable to those obtained through methods involving seismic catalogues and classical zonation models, the spatial pattern of our model is far more detailed. Our model is characterized by areas that are more hazardous and that correspond to mapped active faults, while the previous models yield expected accelerations that are almost uniformly distributed across large regions. In addition, we conducted sensitivity tests to determine the impact on the hazard results of the earthquake rates derived from two magnitude-frequency distribution models for faults and to determine the relative contributions of faults versus distributed seismic activity. We think our model represents an advance for Italy in terms of input data (quantity and quality) and methodology in the field of the fault-based regional seismic hazard modelling.

Description: The multisegment Wasatch fault zone is a well-studied normal fault in the western United States that has paleoseismic evidence of recurrent Holocene surface-faulting earthquakes. Along the 270? km long central part of the fault, four primary structural complexities provide possible along-strike limits to these ruptures and form the basis for models of fault segmentation. Here, we assess the impact that the Wasatch fault segmentation model has on seismic hazard by evaluating the time-independent long-term rate of ruptures on the fault that satisfy fault-slip rates and paleoseismic event rates, adapting standard inverse theory used in the Uniform California Earthquake Rupture Forecast, Version 3, and implementing a segmentation constraint in which ruptures across primary structural complexities are penalized. We define three models with varying degrees of rupture penalization: (1)? segmented (ruptures confined to individual segments), (2)? penalized (multisegment ruptures allowed, but penalized), and (3)? unsegmented (all ruptures allowed). Seismic-hazard results show that, on average, hazard is highest for the segmented model, in which seismic moment is accommodated by frequent moderate (moment magnitude Mw? 6.2–6.8) earthquakes. The unsegmented model yields the lowest average seismic hazard because part of the seismic moment is accommodated by large (Mw? 6.9–7.9) but infrequent ruptures. We compare these results to model differences derived from other inputs such as slip rate and magnitude scaling relations and conclude that segmentation exerts a primary control on seismic hazard. This study demonstrates the need for additional geologic constraints on rupture extent and methods by which these observations can be included in hazard-modeling efforts.

Description: Italy is one of the most seismically active countries in Europe. Moderate to strong earthquakes, with magnitudes of up to ∼ 7, have been historically recorded for many active faults. Currently, probabilistic seismic hazard assessments in Italy are mainly based on area source models, in which seismicity is modelled using a number of seismotectonic zones and the occurrence of earthquakes is assumed uniform. However, in the past decade, efforts have increasingly been directed towards using fault sources in seismic hazard models to obtain more detailed and potentially more realistic patterns of ground motion. In our model, we used two categories of earthquake sources. The first involves active faults, and using geological slip rates to quantify the seismic activity rate. We produced an inventory of all fault sources with details of their geometric, kinematic, and energetic properties. The associated parameters were used to compute the total seismic moment rate of each fault. We evaluated the magnitude–frequency distribution (MFD) of each fault source using two models: a characteristic Gaussian model centred at the maximum magnitude and a truncated Gutenberg–Richter model. The second earthquake source category involves grid-point seismicity, with a fixed-radius smoothed approach and a historical catalogue were used to evaluate seismic activity. Under the assumption that deformation is concentrated along faults, we combined the MFD derived from the geometry and slip rates of active faults with the MFD from the spatially smoothed earthquake sources and assumed that the smoothed seismic activity in the vicinity of an active fault gradually decreases by a fault-size-driven factor. Additionally, we computed horizontal peak ground acceleration (PGA) maps for return periods of 475 and 2475 years. Although the ranges and gross spatial distributions of the expected accelerations obtained here are comparable to those obtained through methods involving seismic catalogues and classical zonation models, the spatial pattern of the hazard maps obtained with our model is far more detailed. Our model is characterized by areas that are more hazardous and that correspond to mapped active faults, while previous models yield expected accelerations that are almost uniformly distributed across large regions. In addition, we conducted sensitivity tests to determine the impact on the hazard results of the earthquake rates derived from two MFD models for faults and to determine the relative contributions of faults versus distributed seismic activity. We believe that our model represents advancements in terms of the input data (quantity and quality) and methodology used in the field of fault-based regional seismic hazard modelling in Italy.