Rare Occurrences of Non‐cascading Foreshock Activity in Southern California

Abstract

Earthquakes preceding large events are commonly referred to as foreshocks. They are often considered as precursory phenomena reflecting the nucleation process of the main rupture. Such foreshock sequences may also be explained by cascades of triggered events. Recent advances in earthquake detection motivates a reevaluation of seismicity variations prior to mainshocks. Based on a highly complete earthquake catalog, previous studies suggested that mainshocks in Southern California are often preceded by anomalously elevated seismicity. In this study, we test the same catalog against the Epidemic Type Aftershock Sequence model that accounts for temporal clustering due to earthquake interactions. We find that 10/53 mainshocks are preceded by a significantly elevated seismic activity compared with our model. This shows that anomalous foreshock activity is relatively uncommon when tested against a model of earthquake interactions. Accounting for the recurrence of anomalies over time, only 3/10 mainshocks present a mainshock‐specific anomaly with a high predictive power.

Immediate Foreshocks Indicating Cascading Rupture Developments for 527 M 0.9 to 5.4 Ridgecrest Earthquakes

“…In most studies, the term “foreshock” is loosely defined, and they are often considered in much larger spatiotemporal scales, that is, over tens of kilometers and/or days of periods (Abercrombie & Mori, 1996; X. Chen & Shearer, 2013; Moutote et al., 2021; Shearer & Lin, 2009; Trugman & Ross, 2019; van den Ende & Ampuero, 2020). The foreshocks that we search in the high‐resolution catalog (Shelly, 2020) are specific events analogous to our immediate foreshocks, and they are selected based on strict constraints in space and time (Figure 4).…”

“…Earthquake foreshocks are one type of possible precursors and their spatiotemporal correlation with the mainshocks suggests that they may help to describe the earthquake rupture preparation process (Kato et al., 2012; Moutote et al., 2021; Ruiz et al., 2014; Trugman & Ross, 2019). However, the general prevalence of foreshocks is less clear and the physical origin of the foreshocks is not well‐understood (Abercrombie & Mori, 1996; Ellsworth & Bulut, 2018; Moutote et al., 2020; Seif et al., 2019; Shearer & Lin, 2009; Tape et al., 2018; van den Ende & Ampuero, 2020).…”

Big Data Seismology

“…In real fault systems, the cascade and preslip models of nucleation are not mutually exclusive and indeed may feedback on one another (Cattania & Segall, 2021; McLaskey, 2019; Noda et al., 2013). Recent observations from high‐resolution earthquake catalogs around the world (Cabrera et al., 2022; Durand et al., 2020; Ellsworth & Bulut, 2018; Feng et al., 2021; Gardonio et al., 2020; Malin et al., 2018; H. Meng & Fan, 2021; Moutote et al., 2021; Sánchez‐Reyes et al., 2021; Shelly, 2020; Trugman & Ross, 2019; M. P. A. van den Ende & Ampuero, 2020; Yao et al., 2020; Yoon et al., 2019) are beginning to bridge the gap between laboratory and field scales by providing more complete and holistic observations of the nucleation process. The diverse range of physical processes highlighted by these recent studies suggest that earthquake nucleation does not follow a simple, uniform trajectory common to all earthquakes, but instead may be complex and highly dependent on the details of the faulting environment and stress regime.…”

Evidence of an aseismic slip continuously driving the 2017 Valparaiso earthquake sequence

“…In the framework of a slow nucleation phase, such foreshock activity is interpreted as small locked asperities that break up as the background aseismic slip accelerates (Ohnaka, 1992;Dodge et al, 1996;McLaskey, 2019). However, analyzing solely the seismicity rate to infer preparatory process before large earthquake is a difficult task (Ross et al, 2019; van den Ende & Ampuero, 2020; Moutote et al, 2021). Indeed, earthquakes are strongly time-and space-clustered (Helmstetter & Sornette, 2003;Marsan & Lengline, 2008) mainly because they interact with each other, making their probability of occurrence dependent on the past seismic activity.…”