Targeted High-Resolution Structure from Motion Observations Over the M6.4 and M7.1 Ruptures of the Ridgecrest Earthquake Sequence

Session: Observations From the 2019 Ridgecrest Earthquake Sequence
Type: Oral
Date: 4/28/2020
Time: 03:30 PM
Room: 115
Description: 

Following the July 4-5 Ridgecrest earthquake sequence, we carried out targeted structure from motion (SfM) surveys over the M6.4 and M7.1 ruptures just south of highway 178. We used small uninhabited aerial vehicles (sUAS) to fly double grids over the target areas, which are each about 3.5 km southwest or south east of the intersection of the two ruptures. The surveys cover approximately 500 m x 500 m areas with an average ground sample distance of 1.5 cm. We used Pix4D to process the data to produce point clouds, orthomosaics and digital surface models. Ground control points (GCPs) were surveyed using real-time kinematic (RTK) GPS and used to constrain the solutions and serve as check points. The first survey took place 5 days after the M6.4 foreshock on 9 July 2019. Surveys have been repeated with decreasing frequency over time, with five surveys taking place in the first month after the earthquake and another survey 80 days after the first survey. Comparison of imagery from before and after the M7.1 earthquake shows variation in slip on the main rupture plane and a small amount of distributed slip across the scene. Cracks can be observed and mapped in the high-resolution imagery, which show en echelon cracking, fault splays and a northeast striking conjugate fault at the M7.1 rupture south of highway 178 and near the dirt road. Initial postseismic results show little fault afterslip, but possible subsidence in the first 7-10 days after the earthquake, followed by uplift that follows a log type decay.

Presenting Author: Andrea Donnellan

Authors