The break of rupture asperities as resolved by distributed acoustic sensing

Jiaxuan Li, Taeho Kim, Nadia Lapusta, Zhongwen Zhan, & Ettore Biondi

Submitted September 11, 2022, SCEC Contribution #12231, 2022 SCEC Annual Meeting Poster #033

Back-projection of high-frequency teleseismic P waves improves our understanding of the temporal and spatial rupture evolution of large earthquakes. Yet, its application to moderate-sized earthquakes is rare since ultra-dense seismic arrays near earthquakes are usually not available. Here, we push the resolution limit of back-projection for moderate-sized earthquakes by converting two pre-existing dark fibers into an ultra-dense seismic array. With about 9,000 channels spanning a total distance of around 90 kilometers, we apply a 3D back-projection imaging and tracked the high-resolution rupture process for the July 8th, 2021, Mw6.0 earthquake in the Antelope Valley, eastern California. We resolve four high-frequency energetic subevents in a 3 km-by-5 km area. We verify their location and origin time by timing their S-wave arrival on several nearby strong-motion stations. By comparing with the moment rate function determined from long-period waveforms, we find that their timings mark the onset of high moment release. We suggest that the high-frequency subevents are related to the initiation/breaking of individual rupture asperities that substantially modulate the overall rupture dynamics. To verify this hypothesis, we perform dynamic rupture simulations by considering a homogeneous planar seismogenic zone containing high-normal-stress patches with locations based on the imaged subevents. Our rupture simulation reproduces several key observations: the moment magnitude, the relatively long rupture duration, the significant rupture slow down before the last and largest subevent, the two local peaks of the moment rate function (with a larger second peak), the time of subevents/breaking of asperities, and the elliptical shape of final slip distribution. The simulation shows both rupture delay and promotion by asperities depending on their properties and stress levels. Since there are numerous other moderate-sized crustal earthquakes showing complex moment-release patterns, such modulation of rupture behavior by local fault heterogeneities may be ubiquitous. Combining the DAS-enabled high-frequency imaging of moderate-sized earthquakes and dynamic rupture simulations, we could form a unique insight into the role of geometrical, stress, and material heterogeneities in earthquake ruptures.

Key Words
DAS, Back-projection, Dynamic Rupture

Citation
Li, J., Kim, T., Lapusta, N., Zhan, Z., & Biondi, E. (2022, 09). The break of rupture asperities as resolved by distributed acoustic sensing. Poster Presentation at 2022 SCEC Annual Meeting.

Related Projects & Working Groups
Seismology