Single-station cross-correlation analysis of ambient seismic noise: application to stations in the surroundings of the 2008 Iwate-Miyagi Nairiku earthquake

Abstract

We introduce the single-station cross-correlation (SC) technique of processing ambient seismic noise and compare its results with the established cross-correlation (CC) and autocorrelation (AC) techniques. While CC is the correlation of the signals of two seismic stations with each other and AC is the correlation of a signal with itself, SC is the correlation of two different components of a single three-component seismic sensor. The comparison of the three different correlation techniques shows that CCs give the best results at frequencies below 0.5 Hz and that SCs give the best results at higher frequencies. In all three processing techniques, ambient seismic noise is correlated in order to reconstruct the Green's function describing the wave propagation between the first and the second sensor. By relating the coda parts of the daily Green's functions with the long-term reference Green's functions, shear wave velocity changes are determined. Here, we apply this technique to the data of 20 seismic stations in the surroundings of the fault zone of the Iwate-Miyagi Nairiku earthquake (M W = 6.9), which occurred on 2008 June 13, UTC (2008 June 14, Japan Standard Time) in the northern part of the Japanese island Honshu. The data range from 2008 January to 2011 June and therefore include the Tohoku earthquake (M W = 9.0), which occurred on 2011 March 11, off the coast of northern Honshu. The data are analysed in five different frequency ranges between 0.125 and 4.0 Hz. The data show coseismic velocity changes for both earthquakes followed by a postseismic velocity recovery. In general, the coseismic velocity changes increase with frequency. For the Iwate-Miyagi Nairiku earthquake, the strongest velocity changes occur close to the fault zone. Quickly recovering coseismic velocity changes can be separated from changes not recovering during the study period. For the Tohoku earthquake, the complete area is affected by coseismic velocity changes. A modelling of the depth of the coseismic velocity changes indicates that the Iwate-Miyagi Nairiku earthquake can be explained either by large shallow velocity changes or by small, but deep changes. For one station, the observations can only be explained by assuming deeper changes. For the Tohoku earthquake, the modelling shows that different parts of the study area are affected in different ways, some showing shallow changes, others deeper changes. Furthermore, seasonal velocity variations occur, which are compatible for the different stations above 0.5 Hz, with velocity maxima in autumn.

Complex Near‐Surface Rheology Inferred From the Response of Greater Tokyo to Strong Ground Motions

“…To average the velocity variations over the two components, we use the method proposed by Hobiger et al () that weights the contribution of the velocity changes with the correlation coefficients after stretching as where c k ( t ) is the correlation coefficient after stretching for the k th component ( Z ‐ E or Z ‐ N ). The variable t is the time for which the velocity variations are computed (e.g., every 6 hr over the 2.5‐month observation period).…”

“…Without necessarily interpreting the phases in the cross correlograms, one can also monitor the temporal evolution of the wave arrival times. AC and SC functions have been used to detect seismic velocity changes during earthquakes (Gassenmeier et al, 2016;Hobiger et al, 2012Hobiger et al, , 2014Hobiger et al, , 2016Richter et al, 2014;Wegler & Sens-Schönfelder, 2007) and volcanic eruptions (De Plaen et al, 2016). However, these studies focused on velocity changes of coda waves at relatively low frequencies (∼0.1 to 4 Hz), making the measurements sensitive to variations occurring within a few kilometers of depth.…”

“…To average the velocity variations over the two components, we use the method proposed by Hobiger et al (2014) that weights the contribution of the velocity changes with the correlation coefficients after stretching as…”

Single‐station monitoring of volcanoes using seismic ambient noise

“…The technique is also applicable to single stations, using one (or all) component of a one‐component (or three‐component) seismometers. The single‐station approach has been successfully applied to study earthquakes [ Sens‐Schönfelder and Wegler , ; Wegler and Sens‐Schönfelder , ; Hobiger et al ., ; Nakahara , ; D'Hour et al ., ].…”

“…The single-station approach has been successfully applied to study earthquakes [Sens-Schönfelder and Wegler, 2006;Wegler and Sens-Schönfelder, 2007;Hobiger et al, 2014;Nakahara, 2014;D'Hour et al, 2015].…”