Methodology for earthquake rupture rate estimates of fault networks: example for the western Corinth rift, Greece

Abstract

Abstract. Modeling the seismic potential of active faults is a fundamental step of probabilistic seismic hazard assessment (PSHA). An accurate estimation of the rate of earthquakes on the faults is necessary in order to obtain the probability of exceedance of a given ground motion. Most PSHA studies consider faults as independent structures and neglect the possibility of multiple faults or fault segments rupturing simultaneously (fault-to-fault, FtF, ruptures). The Uniform California Earthquake Rupture Forecast version 3 (UCERF-3) model takes into account this possibility by considering a system-level approach rather than an individual-fault-level approach using the geological, seismological and geodetical information to invert the earthquake rates. In many places of the world seismological and geodetical information along fault networks is often not well constrained. There is therefore a need to propose a methodology relying on geological information alone to compute earthquake rates of the faults in the network. In the proposed methodology, a simple distance criteria is used to define FtF ruptures and consider single faults or FtF ruptures as an aleatory uncertainty, similarly to UCERF-3. Rates of earthquakes on faults are then computed following two constraints: the magnitude frequency distribution (MFD) of earthquakes in the fault system as a whole must follow an a priori chosen shape and the rate of earthquakes on each fault is determined by the specific slip rate of each segment depending on the possible FtF ruptures. The modeled earthquake rates are then compared to the available independent data (geodetical, seismological and paleoseismological data) in order to weight different hypothesis explored in a logic tree.The methodology is tested on the western Corinth rift (WCR), Greece, where recent advancements have been made in the understanding of the geological slip rates of the complex network of normal faults which are accommodating the ∼ 15 mm yr −1 north-south extension. Modeling results show that geological, seismological and paleoseismological rates of earthquakes cannot be reconciled with only singlefault-rupture scenarios and require hypothesizing a large spectrum of possible FtF rupture sets. In order to fit the imposed regional Gutenberg-Richter (GR) MFD target, some of the slip along certain faults needs to be accommodated either with interseismic creep or as post-seismic processes. Furthermore, computed individual faults' MFDs differ depending on the position of each fault in the system and the possible FtF ruptures associated with the fault. Finally, a comparison of modeled earthquake rupture rates with those deduced from the regional and local earthquake catalog statistics and local paleoseismological data indicates a better fit with the FtF rupture set constructed with a distance criteria based on 5 km rather than 3 km, suggesting a high connectivity of faults in the WCR fault system.

Dynamics of microseismicity and its relationship with the active structures in the western Corinth Rift (Greece)

“…Seismic hazard related to the coastal faults has been studied by Chartier et al (2017) and Boiselet (2014), who integrated the observation that the last major earthquakes in the ZW ruptured blind faults (i.e. Aigion 1995 earthquake; Bernard et al 1997) or faults not identified as a major structure (i.e.…”

Modelling earthquake rupture rates in fault systems for seismic hazard assessment: The Eastern Betics Shear Zone

“…In addition, some of these studies consider the occurrence of multi-fault ruptures as an aleatory uncertainty linked to the randomness of the seismic process (e.g. Chartier et al, 2017Chartier et al, , 2019Field et al, 2014;Working Group On California Earthquake Probabilities, 2003).…”

SHERIFS: Open‐Source Code for Computing Earthquake Rates in Fault Systems and Constructing Hazard Models

“…The logic-tree structure and the input files can be easily modified for a rerun if different parameters need to be tested. This section of the article synthesizes the main steps of the methodology implemented in SHERIFS as presented in Chartier et al (2017). This methodology requires as input data fault section geometries and slip-rate estimates for all the faults of the fault system to calculate the earthquake rupture rates.…”

“…Because R is very difficult to determine, several background hypotheses are meant to be explored. This straightforward definition of the background has been introduced in SHERIFS since the version used in Chartier et al (2017). We hope to encourage the discussion about the expert opinion on the matter of the background seismicity and its effect on the seismic-hazard assessment.…”