Developing a Comprehensive Seismic Catalog Using a Matched Filter Detector During a 2019 Stimulation at Utah FORGE

Abstract

In April 2019, a stimulation was carried out at the Utah Frontier Observatory for Research in Geothermal Energy (FORGE). Microseismicity during this stimulation was monitored using 1) a geophone string and DAS cable in a collocated borehole, 2) a local network of surface broadband sensors and a 305 m shallow borehole geophone, and 3) a surface network of geophones. The detection capabilities of this network were mixed. The most complete catalog, which contains 424 events spanning -2.0 Mw to -0.5 Mw, was determined using the geophone string operated by Schlumberger. However, this catalog is limited by short monitoring duration, which restricts seismic observations to the injection times. Here, we implement a matched-filter detector using a single borehole station within the FORGE footprint to identify small earthquakes (Mw less than 0) which previously went undetected. Matched-filter detectors are widely used to develop comprehensive earthquake catalogs that can provide better estimations of the Gutenberg-Richter b-value, which is a valuable tool in the development of site-specific seismic mitigation strategies and protocols such as Adaptive Traffic Light Systems (ATLS). The goal of this analysis is to use these detections to 1) determine the detection capabilities for the sensors in the shallow borehole, 2) determine the duration of seismic activity associated with the 2019 stimulation, and 3) enhance the catalog to produce a robust b-value estimation. These data provide a workflow for future studies focused on characterizing the seismic hazard near potential Enhanced Geothermal Systems, especially those which are in relatively aseismic areas.