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The Influence of Preexisting Geologic Structures on Coseismic Surface Deformation During the 2019 M7.1 Ridgecrest, California, Earthquake

Description: 

We investigate how preexisting structures influenced the 2019 M7.1 Ridgecrest, California earthquake rupture at the tens-of-kilometers and meter scales by combining field and remote sensing observations, laboratory analysis, and mechanical modeling. At the longest scales, the fault geometry appears to be inherited from the surrounding late Jurassic Independence dike swarm (IDS), mapped with satellite imagery and airborne lidar data. In the field, we observe multiple fracture sets surrounding the dikes, including dike-parallel fractures that add to the pervasive structural fabric that existed prior to fault initiation. Based on the common geometries and observed deformation, we conclude that the Ridgecrest source faults likely evolved through reactivation of IDS structures. Consequently, we show through a series of finite-element models that the inherited fault geometry strongly controlled the coseismic slip distribution, producing elevated slip (~3-4 m compared to <~1 m elsewhere) within a ~12-km-long section of the rupture oriented ~20 degrees more northerly than elsewhere. Part of this maximum slip zone lies within the China Lake Playa where the rupture localized into knife-edge echelon segments separated by meter-scale left steps. We explore surface rupture processes at this length scale using discrete element models, which suggest that the development of such a narrow deformation zone is encouraged by loosely packed granular material that produces minimal dilation during shear. We analyze samples collected from the surface rupture using scanning electron microscopy techniques and find that a sequence of evaporite minerals coat the rupture surface, including halite that flows ductilely around broken clasts of carbonate mud. These observations suggest that the 2019 surface rupture may have reoccupied preexisting fractures, perhaps formed during a previous surface-rupturing earthquake. Over the range of scales considered, combining field, laboratory, and modeling methods illustrates the importance of preexisting structures in controlling where and how earthquake deformation accrues.

Session: Learning Across Geological, Geophysical & Model-Derived Observations to Constrain Earthquake Behavior - II

Type: Oral

Date: 5/1/2024

Presentation Time: 10:45 AM (local time)

Presenting Author: Johanna

Student Presenter: No

Invited Presentation: Yes

Authors