High Temporal Resolution Monitoring of Small Variations in Crustal Strain by Dense Seismic Arrays

Abstract

We demonstrate the feasibility of detecting very weak deformation in the shallow crust with high temporal resolution by monitoring the relative changes in seismic wave velocity (dv/v) using dense arrays of seismometers. We show that the dv/v variations are consistent between independent measurements from two seismic arrays. Dominant peaks in the observed dv/v spectrum suggest that tides and temperature changes are the major causes of daily and subdaily velocity changes, in accordance with theoretical strain modeling. Our analysis illustrates that dv/v perturbations of the order of 10−4, corresponding to crustal strain changes of the order of 10−8, can be measured from ambient seismic noise with a temporal resolution of 1 hr. This represents a low‐cost technique for high precision and high time‐resolution monitoring of crustal deformation that is complementary to existing geodetic measurements and is instrumental in both the detection and understanding of low‐amplitude precursory processes of natural catastrophic events.

Diurnal and Semidiurnal P‐ and S‐Wave Velocity Changes Measured Using an Airgun Source

“…The traveltime changes are divided by the absolute traveltimes d t / t (Figure ), inverse to the relative velocity changes d v / v , are of the order 10 −4 (Figure 9a). These amplitudes of d v / v are of an order similar to the previous observations from active (e.g., Reasenberg & Aki , ) and passive source monitoring (e.g., Mao et al, ).…”

“…However, our velocity change correlate well to the tide in 1-day period (cc = −0.90; Figure 11b) but poorly correlates to the stronger half-day (cc=−0.21; Figure 11c) and broadband (cc = −0.49; Figure 11a) tides. Furthermore, Earth tides are believed to cause instant velocity changes (Mao et al, 2019;Reasenberg & Aki, 1974), which are not observed here. Therefore, the solid Earth tide is unlike the primary cause of the observed velocity changes.…”

“…Diurnal and semidiurnal velocity changes are usually attributed to changes in solid Earth tides (Mao et al, 2019;Reasenberg & Aki, 1974), ocean tides (Yamamura et al, 2003), barometric pressure (Silver et al, 2007;Wang et al, 2008), and air temperature (Mao et al, 2019;Sens-Schönfelder & Larose, 2008). Herein, we compared the average velocity change (Figure 9b) with the tides, air temperature, and air pressure at different periods (Figures 11 and 12).…”

“…Recently, diurnal, semidiurnal, and terdiurnal components in the spectrum of seismic velocity changes have been reported via ambient noise interferometry (Mao et al, 2019). Diurnal and subdiurnal velocity changes may be caused by Earth tides (e.g., Reasenberg & Aki, 1974;Yamamura et al, 2003), barometric loading (e.g., Silver et al, 2007;Wang et al, 2008), or a combination of tides and solar radiation (Mao et al, 2019). Monitoring the diurnal and subdiurnal seismic velocity changes also benefits the extraction of possible short-term precursory signals prior to earthquakes (e.g., Niu et al, 2008).…”

Evidence of Changes of Seismic Properties in the Entire Crust Beneath Japan After the Mw 9.0, 2011 Tohoku‐oki Earthquake

“…This can provide insights not only into the tectonic and volcanic processes (Brenguier, Campillo, et al, ; Brenguier, Shapiro, et al, ; Brenguier et al, ; Chen et al, ; Froment et al, ; Obermann et al, ; Taira & Brenguier, ; Wegler et al, ) but also into some transient fluctuations that are derived from external environmental perturbations (Sens‐Schönfelder & Wegler, ; Meier et al, ; Hillers et al, ; Hillers, Ben‐Zion, et al, ; Wang et al, ). The characteristic depth at which such changes can be monitored varies from meters (Hillers, Retailleau, et al, ; Mao et al, ; Sens‐Schönfelder & Wegler, ) down to dozens of kilometers into the crust (Froment et al, ; Obermann et al, ; Rivet et al, ), through measurements at various periods. Our goal here is to investigate changes down to 40 km in depth at a regional scale after a significant earthquake.…”