Monitoring induced seismic tremor associated with fluid injection/extraction and mechanical operations at the Domo San Pedro geothermal field (Mexico)

Seismic tremor signals were recorded in 2021 by a temporary broadband seismic network deployed in the surroundings of the Domo de San Pedro geothermal field (DSPgf) in Mexico. A network-based covariance matrix approach was used to analyze those tremor-like signals, employing vertical-component data only. Seismic tremors were detected by identifying periods associated with low values of spectral width, defined as the width of the eigenvalue distribution of the network covariance matrix. These tremors occur in frequency bands ranging from 1 to more than 22 Hz, with durations varying from hours to months, and show higher amplitudes at closest stations to the active wells. The spectral characteristics of the DSPgf tremor-like signals reveal similarities to those found in volcanic and glacial environments, such as the presence of harmonic frequencies and spectral gliding. The sources of these tremor signals are located by back-projecting on a 3-D grid the dominant component of the wavefield obtained from the covariance matrix first eigenvector. Tremor locations indicate that the events originate within the zones of influence of the wells where geothermal operations occurred. We categorized four distinct tremor families based on spectral width signatures and compared them with detailed operational records. Our findings reveal that tremors at the DSPgf are associated with geothermal operations such as fluid extraction, wellbore maintenance, fluid re-injection, and changes in injection pressure. We propose a conceptual model of the first order tremor-generating mechanism for each tremor family.