Passive Seismic Investigations of the Valles Caldera during SAGE 2019

Session: Advances in Upper Crustal Geophysical Characterization [Poster]
Type: Poster
Date: 4/29/2020
Time: 08:00 AM
Room: Ballroom
Description: 

The Summer of Applied Geophysical Experience (SAGE) is a month-long field program which provides undergraduate and graduate students with hands-on exposure to geophysical instrumentation, field techniques and data collection. June 2019 was the start of a multi-year geophysical investigation in the Valles Caldera, a 1.2 Ma volcanic caldera that sits along the western margin of the Rio Grande Rift in the Jemez Mountains of New Mexico. Alongside magnetic, gravity, electrical, electromagnetic, distributed temperature sensing and active-source seismic studies, we deployed an array of 5-Hz Magseis Fairfield 3C nodes and recorded continuous passive seismic data for a month. We deployed 40 nodes along two intersecting lines in Valle Grande, a Pleistocene lakebed formed by past obstruction of the Jemez river by volcanic flows. An additional 8 nodes were deployed along the perimeter of the Valle Grande.

An analysis of horizontal-to-vertical spectral ratios reveals a pronounced spectral peak at most locations. Together with independent estimates of shear-wave velocity, the depth to consolidated basement is constrained to between 400 and 800m in the center of Valle Grande, thinning abruptly near the edge of the Valle. We are also performing beamforming and F-K analysis to understand the nature and direction of the ambient noise during the period of data collection. We plan to perform Green’s function cross-correlation analysis to detect surface and body waves for velocity analysis and autocorrelation analysis to image reflectivity beneath the site. We are also parsing the dataset for microseismicity in order to better understand the volcanic and tectonic architecture and current activity levels of the caldera and environs. In addition, we shot several very long (60-second) low-frequency Vibroseis sweeps into the passive array to try and image Moho below the caldera.

Presenting Author: Akram Mostafanejad

Authors