A phase coherence approach to identifying co-located earthquakes and tremor

Abstract

S U M M A R YWe present and use a phase coherence approach to identify seismic signals that have similar path effects but different source time functions: co-located earthquakes and tremor. The method used is a phase coherence-based implementation of empirical matched field processing, modified to suit tremor analysis. It works by comparing the frequency-domain phases of waveforms generated by two sources recorded at multiple stations. We first cross-correlate the records of the two sources at a single station. If the sources are co-located, this cross-correlation eliminates the phases of the Green's function. It leaves the relative phases of the source time functions, which should be the same across all stations so long as the spatial extent of the sources are small compared with the seismic wavelength. We therefore search for cross-correlation phases that are consistent across stations as an indication of co-located sources. We also introduce a method to obtain relative locations between the two sources, based on back-projection of interstation phase coherence. We apply this technique to analyse two tremor-like signals that are thought to be composed of a number of earthquakes. First, we analyse a 20 s long seismic precursor to a M 3.9 earthquake in central Alaska. The analysis locates the precursor to within 2 km of the mainshock, and it identifies several bursts of energy-potentially foreshocks or groups of foreshocks-within the precursor. Second, we examine several minutes of volcanic tremor prior to an eruption at Redoubt Volcano. We confirm that the tremor source is located close to repeating earthquakes identified earlier in the tremor sequence. The amplitude of the tremor diminishes about 30 s before the eruption, but the phase coherence results suggest that the tremor may persist at some level through this final interval.

Microseismic Monitoring of Stimulating Shale Gas Reservoir in SW China: 1. An Improved Matching and Locating Technique for Downhole Monitoring

“…If the hypocentral distance between the master‐slave event pair is significantly smaller than both the event receiver distance and the scale length of the velocity heterogeneity, the similar raypaths between the two events and a common receiver leads to nearly identical Green's functions. Consequently, the cross correlation eliminates the phases of the Green's function, leaving the relative phases of the source time functions of two closely located events (e.g., Hawthorne & Ampuero, ). Meanwhile, it also naturally accounts for any variations due to the radiation pattern of a typical double‐couple source mechanism of shear sources.…”

Towards a standard typology of endogenous landslide seismic sources

“…It must be noted that the network geometry in the case of landslides is constrained by the site configuration. Indeed, the maintenance of seismic sensors may be very challenging when installed on the moving parts of the landslide; therefore, an installation on the most stable parts of the landslide or at its vicinity is often preferred for permanent monitoring (Spillmann et al, 2007;Helmstetter and Garambois, 2010;Walter et al, 2017). During field campaigns, maintenance of sensors installed on the unstable slopes is possible and often realized (Gomberg et al, 2011;Walter et al, 2012;Tonnellier et al, 2013).…”

“…Gomberg et al (1995) installed seismometers on the Slumgullion slow-moving landslide (Colorado, USA) in order to understand the mechanical processes taking place during landslide deformation. Further studies used the same method for several slope configurations (hard or soft rocks, soils, very slow to rapid movements) but also investigated the possible links between the displacement rate and the seismic energy release (Spillmann et al, 2007;Helmstetter and Garambois, 2010;Walter et al, 2012Walter et al, , 2013bTonnellier et al, 2013). Helmstetter and Garambois (2010) correlated the seismic response of the Séchilienne rockslide with the surface displacement rate and the rainfall amount.…”

“…Further studies used the same method for several slope configurations (hard or soft rocks, soils, very slow to rapid movements) but also investigated the possible links between the displacement rate and the seismic energy release (Spillmann et al, 2007;Helmstetter and Garambois, 2010;Walter et al, 2012Walter et al, , 2013bTonnellier et al, 2013). Helmstetter and Garambois (2010) correlated the seismic response of the Séchilienne rockslide with the surface displacement rate and the rainfall amount. The analysis of the seismic waves generated by landslides allows for monitoring spatiotemporal changes in the stress-strain field in the material from the scale of microscopic internal damage (Dixon et al, 2003;Michlmayr et al, 2012;Smith et al, 2017) to the initiation (e.g., pre-failure) of large ruptures (Amitrano et al, 2005;Yamada et al, 2016b;Poli, 2017;Schöpa et al, 2018).…”

Downhole Microseismic Source Location Based on a Multi‐Dimensional DIRECT Algorithm for Unconventional Oil and Gas Reservoir Exploration

“…Compared to surface monitoring, the obvious advantage of downhole microseismic monitoring is that the detection is nearer the reservoir leading to a high S/N ratio, many more P and S waves, etc. for determining accurate event locations (Song et al, 2013;Chen et al, 2017;Hawthorne and Ampuero, 2017). Fig.…”