Foreshocks, Aftershocks, and Faulting Complexity: the 2019 Ridgecrest Earthquake Sequence in High Resolution

David R. Shelly

Submitted August 15, 2019, SCEC Contribution #9770, 2019 SCEC Annual Meeting Poster #267 (PDF)

Poster Image: 
The 2019 Ridgecrest earthquake sequence provides a fascinating example of earthquake interaction processes and faulting complexity, captured by modern seismic and geodetic networks. Notable features of the sequence include 1) a rich foreshock sequence, including the July 4, M 6.4 event and its foreshocks; 2) apparent multi-fault rupture of the M 6.4 event, with two nearly perpendicular fault segments activated; and 3) complexity of the July 6, M 7.1 mainshock rupture, which included multiple splays at the NW and SE rupture tips, and apparently ruptured both NW and SE of the NW-striking limb of the earlier M 6.4 foreshock.

Here, I use cross-correlation and double-difference relocation to detect and precisely locate additional uncatalogued events, leveraging thousands of earthquakes routinely cataloged by the Southern California Seismic Network (SCSN) as waveform templates. Preliminary efforts detect and precisely locate about twice the number of routinely cataloged events. These preliminary results suggest that the foreshocks preceding the M 6.4 event were concentrated near the intersection of the two main faults, near the bottom of the seismogenic zone. The M 6.4 aftershock sequence shows pronounced spatial “holes,” which may reflect areas of major co-seismic slip. The M 7.1 event nucleated near the northernmost aftershocks from the M 6.4, a zone which became highly active following a M 5.4 event ~16 hours prior to the M 7.1 mainshock. The M 7.1 ruptured either through or around the NW-striking limb of M 6.4 rupture, expanding the earlier rupture zone both to the NW and SE. This high-resolution catalog will provide a basis for examining earthquake interaction and rupture physics in three dimensions.

Key Words
foreshocks, aftershocks, earthquake triggering, rupture dynamics, earthquake relocation, earthquake detection

Citation
Shelly, D. R. (2019, 08). Foreshocks, Aftershocks, and Faulting Complexity: the 2019 Ridgecrest Earthquake Sequence in High Resolution. Poster Presentation at 2019 SCEC Annual Meeting.


Related Projects & Working Groups
Ridgecrest Earthquakes