Evidence of Previous Late Quaternary Faulting Along the 2019 Ridgecrest Earthquake Ruptures

Session: Observations From the 2019 Ridgecrest Earthquake Sequence
Type: Oral
Date: 4/28/2020
Time: 02:30 PM
Room: 115
Description: 

The July 2019 Ridgecrest earthquake sequence in southern California has been characterized as surprising because no continuous faults were mapped in the area prior to these events. Just ~30% of the rupture occurred on mapped faults of the Airport Lake, Little Lake and unnamed fault zones. Upon more detailed inspection of pre-event topography (2-m resolution digital elevation model), imagery and field observations, we document the signature of active faulting in the landscape along the entire fault system, indicating it has been active in the Quaternary. Scarps, deflected drainages and lineaments and contrasts in topography, vegetation and ground color are records of recent fault slip on subparallel strands, consistent with patterns of the wide and complex 2019 surface ruptures. The pre-2019 neotectonic features preserved from paleo events are commonly short (<2 km), discontinuous and display a left-stepping en echelon pattern along both the M6.4 and M7.1 ruptures. Field observations also reveal tufa lineaments and fractured, faulted and sheared Quaternary deposits. Not all mapped fault strands ruptured in 2019. Neotectonic features are better preserved outside of late Pleistocene lake basins. Within the China Lake Basin and Salt Wells Valley, where strike-slip displacement was more prevalent, subtle features, such as tonal and vegetation lineaments and contrasts, were more common. Preservation may also be related to the style of deformation. Scarps and topographic lineaments are better preserved in the landscape at the ends of the rupture where vertical motion was more common in 2019. These observations serve to motivate more detailed study elsewhere in the region where future surface-rupturing earthquakes may occur. In addition, the coseismic ruptures of the Ridgecrest earthquakes illustrate how mapping complex distributed fault systems from neotectonic features presents an on-going challenge to fault characterization for seismic hazard assessments.

Presenting Author: Jessica A. T. Jobe

Authors