Group B, Poster #100, Earthquake Geology

Fault Mapping in Trona, West Searles Valley, San Bernardino County as a result of the 2019 Trona-Ridgecrest Earthquake Sequence, Part 1

Miles H. Wagner
Poster Image: 

Poster Presentation

2022 SCEC Annual Meeting, Poster #100, SCEC Contribution #12407 VIEW PDF
Mapping of the Trona-Ridgecrest Earthquake Sequence began 7/5/19 in Trona for Initial Damage Estimates (IDE). First faulting was marked at the Garlock Fault on Trona Road, continuing 7/6 in Searles Valley. Fault mapping as part of the IDE continued through 7/8. Additional mapping continued through October 2020. We used Garmin GPSmap 60CSx, 62stc, 64s, and 66st; Brunton compasses for location, orientation, strike and slip, with cameras; USGS topo maps for field locations with electronic data transferred to ArcGIS Desktop 10.8.x. Besides the authors Searles Valley Working Group volunteers included geologists, professors, graduate and undergraduate geology students, and other volunteers. Approx...imately 20 days by ~20 volunteers conducted over 100 staff days of field work. Data was collected and compiled daily. Reviews determined next objectives. Data collected included fault trace points, route tracking (not displayed), photo locations, and surface ruptures/fractures.
Area exploration was based on field staff, prior coverage, analysis of our data and other surveillance materials. Local residents provided locations of new fractures. Research material was consulted for additional survey areas. Restrictions limiting our survey abilities included weather and geographic accessibility. We were unable to access locations within China Lake NAWS or within Searles Valley Mining property.
Accurate maps of fractures and other features show fracture start and end points and every 2m of fracture. Start and ends were marked with a 90⁰ offset. Photos were taken of most points/fractures. Measurements recorded offset, uplift, strike, slip and dip as available. Data was transferred daily. Initially data storage was limited by older Garmin memory capacity. Newer Garmin’s allowed a full day of mapping in the heat without having to download data during a survey. Fault zones ranged from a single fracture to areas with extensive short en-echeloned fractures over 200 m in length or more. All were surveyed on foot.
Several map series were created, each more detailed. Current maps include all relevant collected data. Data is available upon request for qualified researchers.
We conclude that on-the-ground field work is necessary to accurately map seismic events, including creep-induced fracturing occurring weeks and/or months after the main event. Use of proven data collection methods instead of unproven, untested equipment provided accurate, readily available data.