Fault System-Based Probabilistic Seismic Hazard Assessment of a Moderate Seismicity Region: The Eastern Betics Shear Zone (SE Spain)

Abstract

Including faults as seismogenic sources in probabilistic seismic hazard assessments (PSHA) has turned into a common practice as knowledge of active faults is improving. Moreover, the occurrence of earthquakes in multi-fault ruptures has evidenced the need to understand faults as interacting systems rather than independent sources. We present a PSHA for the Southeastern Spain obtained by including the faults of a moderate seismicity region, the Eastern Betics Shear Zone (EBSZ) in SE Spain, as the main seismogenic sources in two separate source models, one considering background seismicity. In contrast with previous studies in Spain, earthquake occurrence of the EBSZ system is modeled considering different hypotheses of multi-fault ruptures at the whole fault system scale and weighted in a logic tree. We compare the hazard levels with those from an area source PSHA and a previous fault-based approach. The results show a clear control of the EBSZ faults in the seismic hazard for all return periods, increasing drastically the hazard levels in the regions close to the fault traces and influencing up to 20 km farther with respect to the area source PSHA. The seismic hazard is dependent on the fault slip rates as peak ground accelerations and territorial extension of the fault influence appear higher around the Alhama de Murcia and Carboneras faults, while lower slip rate faults (Palomares Fault) show minor contribution to the hazard. For the return period of 475 years and near-fault locations, our models are more consistent with the ground motion values reached in the 2011 Mw 5.2 Lorca event than the building code or national seismic hazard map, which suggest that our fault system-based model performs more accurate estimations for this return period. Fault data, mainly slip rates, and its uncertainties have a clear impact on the seismic hazard and, for some faults, the lack of detailed paleoseismic studies can compromise the reliability of the hazard estimations. This, together with epistemic uncertainties concerning the background seismicity, are key discussion points in the present study, having an impact on further research and aiming to serve as a case example for other low-to-moderate seismicity regions worldwide.

Geologic and geodetic constraints on the seismic hazard of Malawi’s active faults: The Malawi Seismogenic Source Database (MSSD)

“…Typically, seismogenic sources were developed by considering the historical and instrumental records of earthquakes, however: (1) the relatively short duration of these records imply they are not necessarily representative of a region's long term seismicity (e.g., Hodge et al, 2015;Stein et al, 2012), and (2) it is often unclear how this record should be used to parameterize a seismogenic source's spatial extent (Helmstetter and Werner, 2012) and maximum expected earthquake magnitude (Poggi et al, 2017). Therefore, it is now common to also incorporate fault-based seismogenic sources into PSHA, which combine geologic, paleoseismic, and/or geodetic information to describe the magnitude and frequency of earthquakes on known active faults (e.g., Gómez-Novell et al, 2020;Morell et al, 2020;Pace et al, 2016;Pagani et al, 2020;Stirling et al, 2012).…”

Fault-based Probabilistic Seismic Hazard Analysis in Regions with Low Strain Rates and a Thick Seismogenic Layer: A Case Study from Malawi

“…PSHA using fault-based sources is therefore increasingly popular, and in particular, the use of inversion techniques that constrain on-fault magnitude-frequency distributions (MFDs) by balancing geodetic, geologic, and seismological data (Field et al, 2014(Field et al, , 2021Geist & Parsons, 2018;Chartier et al, 2019). However, it is challenging to reconcile earthquake rates from these data in low strain rate (Cox et al, 2012;Hodge et al, 2015;Vallage & Bollinger, 2020), and yet it is these regions where estimated seismic hazard levels are particularly sensitive to assumptions about fault geometry and segmentation (Hodge et al, 2015;DuRoss et al, 2016;Visini et al, 2020;Gómez-Novell et al, 2020;Valentini et al, 2020;Goda & Sharipov, 2021).…”

Characterization of the shallow subsurface structure across the Carrascoy Fault System (SE Iberian Peninsula) using P-wave tomography and Multichannel Analysis of Surface Waves

“…The EBSZ is an approximately 450km long network of NE-SW-oriented faults (Banda and Ansorge, 1980) that runs from the Alboran Sea to the Mediterranean Sea (De Larouzière et al, 1988;Silva et al, 1993;Silva, 1994). The EBSZ is considered the most active fault system in the Iberian Peninsula (García-Mayordomo, 2005;García-Mayordomo et al, 2007;Gómez-Novell et al, 2020). This area is characterized by an intense earthquake activity which has caused significant damage during historical times (e.g.…”

“…This area is characterized by an intense earthquake activity which has caused significant damage during historical times (e.g. Gómez-Novell et al, 2020) (e.g. the 1518 AD Vera (VII-IX) (e.g.…”