Poster #116, Stress and Deformation Over Time (SDOT)

Preseismic and Post-seismic Transient Strain Anomaly Patterns Before and After the 2019 Ridgecrest Earthquake Sequence

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Poster Presentation

2020 SCEC Annual Meeting, Poster #116, SCEC Contribution #10763
Using cGPS displacements of Network of the Americas (NOTA), we quantify horizontal transient strain anomalies in regions near the epicenters of the 2019 Ridgecrest Earthquake Sequences. The preseismic seasonal strain changes in the regions repeat reliably in years between 2008 and 2019. For instance, our transient horizontal strain solution highlights that extensional dilatational strain anomaly patterns develop in every late spring in the last 12 years on and surrounding regions of the epicenters of the 2019 events, including in June 2019, a month prior to the 2019 Ridgecrest events. In addition to the extensional dilatational strain, our model displacement field shows a development of a ri...ght-lateral shear zone along NW-trending planes in every late spring across the region of the epicenters.

We further quantify the full horizontal transient fields in the regions near Ridgecrest following the 2019 Ridgecrest Earthquake Sequence to investigate the influence of the post-seismic relaxation on the adjacent fault zones. In June 2020, two large earthquakes occurred within the region of our analysis: the M 5.5 earthquake of June 3 in Ridgecrest region and the M 5.8 earthquake of June 24 near the Lone Pine fault zone, which is about 85km NNW of Ridgecrest. Our horizontal transient strain solution shows that the post-seismic effect of the 2019 events has been lasting up to the present and has been perturbing the typical seasonal horizontal strain patterns. In May 2020, a month prior to the M 5.5 and M 5.8 events, our solution predicts extensional dilatational strain in both of the epicenter regions of the 2020 earthquakes. Note that before the 2019 events, contractional dilatation typically developed in the region surrounding the epicenter of the M 5.8 event in late spring. Furthermore, a zone of right-lateral shear is significantly enhanced in Ridgecrest region in the late spring of 2020 following the 2019 events.

These results are consistent with the 2019 Ridgecrest Sequence being triggered by the repeating seasonal strain dilatation and shear patterns, captured by cGPS. Furthermore the post-seismic signals following the 2019 Ridgecrest events have enhanced extensional dilatation and shear patterns throughout Ridgecrest and further north along the Lone Pine fault zone.

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