The 2019 M6.4 and M7.1 Ridgecrest Earthquake Sequence in the eastern California Shear Zone: Overview of Tectonic and Seismological Lessons
Abstract
The 2019 M6.4 and M7.1 Ridgecrest earthquakes are the latest in a series of major earthquakes in the eastern California shear zone (ECSZ). They ruptured the Little Lake fault zone and aftershocks extended from the Garlock fault in the south, to the southern end of the 1872 M7.5 Owens Valley earthquake rupture. Previously, the 1992 M7.3 Landers and the 1999 M7.1 Hector Mine earthquakes ruptured the southern part of the ECSZ zone. The 1947 Mw6.5 Manix earthquake occurred midway between the Hector Mine/Landers sequences and the Ridgecrest sequence. To the north, the 1872 M7.5 Owens Valley earthquake ruptured 120 km in length from the north edge of the Coso range and extended north of Big Pine. This current sequence abuts the 1995 (M5.8 and M5.4) Ridgecrest sequence. The geodetically measured long-term dextral shear across the ECSZ is 7 to 10 mm/yr.
The Ridgecrest foreshock-mainshock sequence so far includes more than 110,000 earthquakes along orthogonal SW and NW trends. A M4 foreshock preceded the M6.4 event by 30 minutes and subsequent aftershocks that formed an L-shaped pattern. About 34 hours later a M5.0 foreshock followed within 3 minutes by the M7.1. The M7.1 event formed a bilateral aftershocks distribution extending from the M7.1 epicenter 20 km northwest and 40 km southeast. The depths extended to 10-12 km. The focal mechanisms are mostly strike slip with a few dip-slip events, consistent with the regional north-south Shmax tectonic stress field. The earthquake sequence's statistical parameters remained fairly constant with time. The b-value was approximately 0.74 suggesting lower productivity of smaller events. The 2019 sequence is characterized by: 1) Very complex 3D crustal deformation field that suggests the presence of a principal slip surface surrounded by a few kilometer-wide crustal deformation zone; 2) Intense initial activity of foreshocks, mainshocks, and aftershocks, which was followed by rapid decay. The rate of decay is consistent with the elevated heat flow in the region; 3) Triggering of at least three distant seismicity clusters; the first in a step-over along the Garlock fault (60 km to the west), the second near Olancha in southern Owens Valley (60 km to the north), and the 3rd in Panamint Valley (40 km to the east). These clusters raised concerns about possible triggering of more activity along these faults.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.S34C..01H
- Keywords:
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- 7299 General or miscellaneous;
- SEISMOLOGY