Work

Continuous Aftershock Hum for over Ten Days Following the 2019 Ridgecrest, California, Earthquakes Observed with Borehole Seismometers

Year: 2025

Type: article

Abstract: Seismograms from two borehole seismometers near the 2019 Ridgecrest, California, aftershock sequence do not return to pre-mainshock noise levels for over ten days after the M 7.1 Ridgecrest mainshock. The observed distribution of root mean square amplitudes in these records can be explained with the Reasenberg and Jones (1989) aftershock occurrence model, which implies a continuous seismic “hum” of overlapping aftershocks of M > −2 occurring at an average rate of 10 events per second after ten days, which prevents observing the background aseismic noise level at times between the body-wave arrivals from cataloged and other clearly observed events. Even after the borehole noise levels return at their quietest times to pre-mainshock conditions, the presence of overlapping low-magnitude earthquakes for 80 days is implied by waveform cross-correlation results provided using the matrix profile method. These results suggest a hidden frontier of tiny earthquakes that potentially can be measured and characterized even in the absence of detection and location of individual events.

Source: Seismological Research Letters

DOI: 10.1785/0220250017

Authors: Peter M. Shearer, Nader Shakibay Senobari

Institutions: Scripps Institution of Oceanography, University of California San Diego, University of California, Riverside

Language: English

Topic: earthquake and tectonic studies

Subfield: Geophysics

Field: Earth and Planetary Sciences

Domain: Physical Sciences

Open Access status: hybrid

Funders: National Science Foundation, Southern California Earthquake Center, U.S. Geological Survey