Stochastic Generator of Earthquakes for Mainland France

Mainland France is characterized by low-to-moderate seismic activity, yet it is known that major earthquakes could strike this territory (e.g., Liguria in 1887 or Basel in 1356). Assessing this French seismic hazard is thus necessary in order to support building codes and to lead prevention actions towards the population. The Probabilistic Seismic Hazard Assessment (PSHA) is the classical approach used to estimate the seismic hazard. One way to apply PSHA is to generate synthetic earthquakes by propagating information from past seismicity and building various seismic scenarios. In this paper, we present an implementation of a stochastic generator of earthquakes and discuss its relevance to mimic the seismicity of low-to-moderate seismic areas. The proposed stochastic generator produces independent events (main shocks) and their correlated seismicity (only aftershocks). Main shocks are simulated first in time and magnitude considering all available data in the area, and then localized in space with the use of a probability map and regionalization. Aftershocks are simulated around main shocks by considering both the seismic moment ratio and distribution of the aftershock’s proportion. The generator is tested with mainland France data.

Propagation of epistemic uncertainty in magnitude–frequency relations through PSHA using predictive distributions

The current practice of Probabilistic Seismic Hazard Analysis (PSHA) considers the inclusion of epistemic uncertainties involved in different parts of the analysis via the logic-tree approach. Given the complexity of modern PSHA models, numerous branches are needed, which in some cases leads to concerns regarding performance issues. We introduce the use of a magnitude exceedance rate which, following Bayesian conventions, we call predictive exceedance rate. This rate is the original Gutenberg–Richter relation after having included the effect of the epistemic uncertainty in parameter β. The predictive exceedance rate was first proposed by Campbell but to our best knowledge is seldom used in current PSHA. We show that the predictive exceedance rate is as accurate as the typical logic-tree approach but allows for much faster computations, a very useful property given the complexity of some modern PSHA models.

Rethinking the Seismic History of the Gulf of Patti (Northeast Sicily, Italy): New Insights from the Local Historical Archives

Improving the knowledge of the seismic history of a region plays a key role in the evaluation of recurrence relations for probabilistic seismic hazard analyses. In this study, we present the results of an investigation carried out in two local historical archives in northeast Sicily, Italy. Several letters, petitions, and reports describing the effects of some earthquakes that occurred between the seventeenth and the eighteenth centuries in the Gulf of Patti area were found and analyzed. This contributed in filling the knowledge gap about a series of moderate-to-large seismic events that were overshadowed by catastrophic earthquakes with major impacts both on human losses and cultural heritage. We describe this experience in the hope that other historians will take up the work, looking for other northeast Sicily local archives to investigate because we believe this is the right way toward a better definition of the seismic history of one of the most seismically active regions of Italy.

Site Specific Probabilistic Seismic Hazard Model for Isfahan, Iran: Estimates and Uncertainties

We present a seismic source characterization model for the probabilistic seismic hazard assessment (PSHA) of the Isfahan urban area, Iran. We compiled the required datasets including the earthquake catalogue and the geological and seismotectonic structure and faults systems within the study region to delineate and characterize seismic source models. We identified seven relatively large zones that bound each region with similar seismotectonic characteristics and catalogue completeness periods. These regions were used for calculating the b-value of the Gutenberg-Richter magnitude recurrence relationship and for estimating the maximum magnitude value within each region. The recurrence parameters were then used to build a spatially varying distributed seismic source model using a smoothed kernel. Additionally, based on a fault database developed in this study and on a local expert’s opinion about their slip velocity, an active faults based model is also created. We further performed sets of sensitivity analyses to find stable estimates of the ground motion intensity and to define alternative branches for both the seismogenic source and ground motion prediction models. Site amplification is considered based on a Vs30 map for Isfahan compiled within this study. The alternative source and ground motion prediction models considered in the logic tree of this study are then implemented in the software Open Quake to generate hazard maps and uniform hazard spectra for return periods of interest. Finally, we provide a detailed comparison of the PSHA outcomes of the current study both with those presented in the 2014 Earthquake Model of Middle East (EMME14) and with the national seismic design spectrum to further discuss the discrepancies between hazard estimates from site-specific and regional PSHA studies.

Probabilistic Seismic Hazard Analysis Based on Arias Intensity in the North–South Seismic Belt of China

ABSTRACT Arias intensity (IA), as an important seismic parameter, which contains the information of amplitude, frequencies, and duration of ground motion, plays a crucial role in characterizing seismic hazard such as earthquake-induced landslides. In this article, we conducted probabilistic seismic hazard analysis (PSHA) based on IA in China’s north–south seismic belt. We adopted the seismic sources and seismicity parameters used in the fifth generation of the Seismic Ground Motion Parameter Zoning Map of China, and two ground-motion model of IA. The results show that the values of IA are greater than 0.11 m/s in most regions of the north–south seismic belt. The provincial capital cities and most prefecture-level cities in the seismic zone are located in the region with IA-values greater than 0.32 m/s. The values of IA are above 0.54 m/s in the region around the main fault zone. This means that the north–south seismic belt is prone to extremely high-seismic hazard, particularly earthquake-induced landslides. Therefore, it is important to strengthen the evaluation and prevention of earthquake-induced landslides in this area. As we have found significant differences in the values of IA calculated from different ground-motion model, it is necessary to study the ground-motion model of IA for the western geological environment of China. In addition, the PSHA based on IA gives more consideration to the influence of large earthquakes than that based on peak ground acceleration. Therefore, IA plays an important role in seismic design of major engineering projects. The results of this article are of great scientific significance for understanding the seismic hazard of the north–south seismic belt.