The Normal Faulting 2020 Mw5.8 Lone Pine, Eastern California Earthquake Sequence

The 2020 Mw5.8 Lone Pine earthquake sequence started with foreshocks on 22^nd of June 2020 about 18 km south-southeast of Lone Pine in Owens Valley, eastern California.The largest event in this foreshock sequence had a magnitude of Mw4.6, with a hypocenter at ~5 km depth, and exhibited normal faulting. It was followed about 40 hours later on the 24^th June 2020 by a Mw5.8 mainshock, at ~7 km depth. The mainshock is the largest normal faulting event in California in decades. During the following 30 days, the M5.8 event was followed by more than 1000 aftershocks in the magnitude range from M1.3 to M4.6, and extending from 3 km to 11 km depth, which outlined the mainshock rupture. The off-fault locations of some of the aftershocks also suggest activation of nearby steeply dipping faults. This sequence was located beneath Owens Lake, to the east of the mapped Owens Valley fault. The whole sequence was located about 20 miles to the north of the 2019 M7.1 Ridgecrest aftershock zone.

The mainshock exhibited normal faulting on a plane striking 330° or north-northwest, and dipping 60° to 65° to the north-northeast. The aftershocks form a dipping cloud, which is consistent with the mainshock rupture. The lack of near-field data and the small size of the mainshock make it difficult to determine the extent of a finite source. The source duration was approximately 3 to 5 s. The aftershock zone covers an area of about 3 to 4 km in diameter, mostly extending down dip and almost unilaterally to the north-northwest.

The largest previous earthquake to occur in this region was the 1872 Mw7.5 Owens Valley earthquake. It caused more than 100 km long surface rupture along the Owens Valley fault, including the segment located along the western shoreline of Owens lake. No surface rupture has been reported along the 1872 scarps for the 2020 M5.8 mainshock although the dipping rupture zone of the M5.8 mainshock projects to the surface in that same general area.