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Spatio-temporal foreshock evolution of the 2019 M 6.4 and M 7.1 Ridgecrest, California Earthquakes

Hui Huang, Roland Bürgmann, Lingsen Meng, Kang Wang, & Baptiste Rousset

Published August 15, 2019, SCEC Contribution #9723, 2019 SCEC Annual Meeting Poster #260

The 2019 M 7.1 Ridgecrest, California earthquake ruptured in a complex multi-segment fault system in the Eastern California Shear Zone. The mainshock was preceded by an intense foreshock sequence, including a large M 6.4 event. The aftershocks of the M 6.4 event illuminated both NW- and NE-trending fault segments, while aftershocks of the M 7.1 event were mainly distributed along the NW direction. The different fault segments involved in the M 6.4 and M 7.1 events provide a good opportunity to investigate how earthquake sequences evolve in complex fault systems, which is important for improved understanding of fault interactions and earthquake triggering. Here, we apply the matched-filter detection method to obtain a more complete and precisely relocated foreshock dataset than the local SCSN catalog. The results show a short phase of earthquake acceleration (~31 minutes) before the M 6.4 event. These preceding events were aligned along the NW direction, implying that the M 6.4 rupture may have initiated on the NW fault segment, before rupturing the primary NE segment. Repeating earthquakes were identified among the foreshock sequence, which might suggest weak small-scale aseismic transients involving slow slip and/or fluid flow. The early aftershock zone of the M 6.4 event rapidly expanded but shows no clear migration towards the M 7.1 hypocenter. However, after a M 5.36 event that occurred in between the M 6.4 and M 7.1 events, a burst of subsequent small earthquakes migrated towards the M 7.1 epicenter for ~25 minutes and 1.3 km (~74 km/day). This rapid migration might suggest afterslip or fluid flow transients, which contributed to load the M 7.1 hypocenter. In our ongoing analysis we hope to consider nearby GPS and strainmeter data to better constrain the possible deformation processes accompanying the foreshock sequence.

Huang, H., Bürgmann, R., Meng, L., Wang, K., & Rousset, B. (2019, 08). Spatio-temporal foreshock evolution of the 2019 M 6.4 and M 7.1 Ridgecrest, California Earthquakes. Poster Presentation at 2019 SCEC Annual Meeting.

Related Projects & Working Groups
Ridgecrest Earthquakes