Measurements of Tilt from Triangular Bench Mark Arrays Installed Within Long Valley Caldera in the 1980s

Kaitlan Q. Elizondo, & Jascha Polet

Published August 13, 2017, SCEC Contribution #7546, 2017 SCEC Annual Meeting Poster #228

Ground tilt and broad deformation within Long Valley Caldera, east central California, has been consistently observed due to magmatic movement beneath the surface. In the early 1980’s, USGS scientists and Arthur G. Sylvester from UCSB, established a network of nine dry tilt arrays around the resurgent dome to monitor inflation by triangulation. Each dry tilt array consists of a primary and a redundancy set of three permanent benchmarks placed in an equilateral triangle with side lengths of about 35 to 40 meters. Over the course of a geophysics field class in July of 2017, we measured three of these arrays on the south side of the dome: Convict Lake, Hot Creek Gorge, and Escape Route. One of the redundancy monuments of the Escape Route array was found to have been destroyed. Students performed high precision measurements using total stations and real time kinematic (RTK) GPS to record elevation, and with the GPS equipment also latitude and longitude. Using the initial baseline measurements and elevations previously recorded in Dzurisin et al. (1982) and Sylvester’s (1985) research, we calculate tilt in microradians and its azimuth from differential elevation changes among the three bench marks of all six arrays at the three sites. We will present our results of these calculations and comparisons with the tilt vectors we calculated for a time span of 35 years with those from Sylvester’s findings in 1985.

Key Words
triangulation, arrays, total station, real time kinematic GPS,

Citation
Elizondo, K. Q., & Polet, J. (2017, 08). Measurements of Tilt from Triangular Bench Mark Arrays Installed Within Long Valley Caldera in the 1980s . Poster Presentation at 2017 SCEC Annual Meeting.

Related Projects & Working Groups
Stress and Deformation Over Time (SDOT)