[S-CG45] Science of slow-to-fast earthquakes

[SCG45-P35] Small-scale Stress Heterogeneity Inferred Many Anti-Repeating Earthquakes in the Sierra Valley, Nevada

Lu Weifan^1,2、*井出 哲¹、Yue Han² (1.東京大学大学院理学系研究科地球惑星科学専攻、2.School of Earth and Space Sciences, Peking University, Beijing, China)

キーワード：反繰り返し地震、シエラバレー、応力不均質、潮汐応答

Repeating earthquakes, which affect overlapping rupture patches with a similar focal mechanism, provide insights into fault creep, earthquake cycle dynamics, triggering, and predictability. Recently, earthquakes with highly anti-correlated waveforms have been systematically reviewed. However, most studies have only observed a small number of anti-repeating earthquake pairs or noted reversals in earthquake focal mechanisms, without connecting these observations to underlying earthquake physics processes. Here we show 37 anti-repeating earthquake pairs (M: 0.18-1.88) in Sierra Valley deep (~32 km) earthquake sequence based on regional waveform analysis. Our high-precision location analysis shows that these anti-repeating earthquakes occur on adjacent faults (separated by ~240 m), with focal mechanisms indicating that normal and thrust earthquakes can occur in a short time intervals. Furthermore, tidal modulation of seismicity in this region suggests a low effective normal stress (~0.1 MPa). We suggest small-scale stress heterogeneity is the mechanism of anti-repeating earthquakes. This variability in stress response highlights the complex dynamics underlying seismicity and offers valuable insights into fault mechanics under variable stress conditions. These findings underscore the necessity of considering both positive and negative components of cross-correlation in earthquake studies to better understand the mechanics of fault systems and improve seismic hazard assessments.