Determination of focal mechanisms of nonvolcanic tremor using <i>S</i> wave polarization data corrected for the effects of anisotropy

Imanishi, Kazutoshi; Uchide, Takahiko; Takeda, Naoto

doi:10.1002/2015gl067249

Cited by 15 publications

(16 citation statements)

References 44 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…In fact, mechanisms determined for LFE template events can include strike-slip type mechanisms [Royer and Bostock, 2014]. Similar source mechanisms have been reported for LFEs in the Nankai subduction zone [Imanishi et al, 2016], where the dominant mechanism is also low-angle thrust, consistent with the large-scale plate motion. Although these estimates may have some uncertainty, if the small-scale focal mechanisms are extremely heterogeneous, then we expect significant non-double-couple (NDC) components in the moment tensors.…”

Section: Discussionsupporting

confidence: 66%

Characteristics of slow earthquakes in the very low frequency band: Application to the Cascadia subduction zone

Ide

2016

JGR Solid Earth

View full text Add to dashboard Cite

Deep tectonic tremors detected in many subduction zones worldwide are often accompanied by very low frequency (VLF) signals, detectable by broadband seismometers but usually hidden in large ambient noise. By stacking broadband seismograms relative to tremor hypocentral times, we can recover the VLF signals. The stacked signals are then inverted to determine a moment tensor solution, using a procedure previously applied to VLF signals in Japan, Taiwan, and Mexico. Here we apply this method to the Cascadia subduction zone, where tremors and slow slip events are clearly observed. As expected, we successfully recover VLF signals for almost the entire tremor region beneath southern Vancouver Island and northern Washington State. The moment tensors are mostly well determined as low‐angle thrust type, but source depths are poorly constrained. The slip direction is slightly rotated counterclockwise with respect to the local plate motion direction, probably due to bending of the subducting plate. The seismic moment measured in VLF band is proportional to the seismic energy of tremors, with a scaled energy of about 3 × 10−9. The widespread observability of VLF signals suggests that the deformation associated with tremors and SSEs is actually a very broadband phenomenon, as suggested by stochastic models.

show abstract

Section: Discussionsupporting

confidence: 66%

Characteristics of slow earthquakes in the very low frequency band: Application to the Cascadia subduction zone

Ide

2016

JGR Solid Earth

View full text Add to dashboard Cite

show abstract

“…Separating S v and S h requires rotating these channels into radial and transverse orientations, and cross‐correlation measurements would need to be recomputed on these rotated seismograms. Additionally, we would need to correct for anisotropy, which can significantly distort S wave polarization directions [e.g., Imanishi et al ., ].…”

Section: Methods Discussion and Future Workmentioning

confidence: 99%

A new strategy for earthquake focal mechanisms using waveform‐correlation‐derived relative polarities and cluster analysis: Application to the 2014 Long Valley Caldera earthquake swarm

et al. 2016

View full text Add to dashboard Cite

In microseismicity analyses, reliable focal mechanisms can typically be obtained for only a small subset of located events. We address this limitation here, presenting a framework for determining robust focal mechanisms for entire populations of very small events. To achieve this, we resolve relative P and S wave polarities between pairs of waveforms by using their signed correlation coefficients—a by‐product of previously performed precise earthquake relocation. We then use cluster analysis to group events with similar patterns of polarities across the network. Finally, we apply a standard mechanism inversion to the grouped data, using either catalog or correlation‐derived P wave polarity data sets. This approach has great potential for enhancing analyses of spatially concentrated microseismicity such as earthquake swarms, mainshock‐aftershock sequences, and industrial reservoir stimulation or injection‐induced seismic sequences. To demonstrate its utility, we apply this technique to the 2014 Long Valley Caldera earthquake swarm. In our analysis, 85% of the events (7212 out of 8494 located by Shelly et al. []) fall within five well‐constrained mechanism clusters, more than 12 times the number with network‐determined mechanisms. Of the earthquakes we characterize, 3023 (42%) have magnitudes smaller than 0.0. We find that mechanism variations are strongly associated with corresponding hypocentral structure, yet mechanism heterogeneity also occurs where it cannot be resolved by hypocentral patterns, often confined to small‐magnitude events. Small (5–20°) rotations between mechanism orientations and earthquake location trends persist when we apply 3‐D velocity models and might reflect a geometry of en echelon, interlinked shear, and dilational faulting.

show abstract

“…These LFEs have been clearly located on the plate interface [ Shelly et al ., ; Brown et al ., ]. Focal mechanisms have then been determined for LFEs in Cascadia [ Royer and Bostock , ], Nankai [ Imanishi et al ., ], and Mexico [ Frank et al ., ]. Focal mechanisms for VLF events have also been determined for isolated events in the Nankai [ Ito et al ., , ] and Ryukyu subduction zones [ Ando et al ., ].…”

Section: Introductionmentioning

confidence: 99%

Comparative study of tectonic tremor locations: Characterization of slow earthquakes in Guerrero, Mexico

et al. 2016

View full text Add to dashboard Cite

Deep tectonic tremor in Guerrero, Mexico, has been observed using dense temporal seismic networks (i.e., the Meso‐American Subduction Experiment and Guerrero Gap Experiment (G‐GAP) arrays) during two different time periods. We apply a set of seismic waveform analysis methods to these data sets to constrain the locations of tremors and determine the associated moment tensors. First we detect and locate the tremors. Next, very low frequency (VLF) signals are identified by stacking waveform data during tremor bursts, and their moment tensors are determined. Finally, to better investigate the link between tremors and VLF earthquakes, we detect VLF events using a matched filtering algorithm to search continuous seismic records. None of the 11 VLF events detected by this method occurred in the absence of tremor bursts suggesting they are indeed part of the same phenomena. Unlike previous investigations, our results for the G‐GAP period reveal that downdip tremor activity (i.e., in the so‐called “sweet spot”) is segmented into two patches separated by 40 km in the along‐trench direction, indicating possible variations in the geometry of the plate interface and/or slab effective pressure. Moment tensors of VLF signals are consistent with shear slip on the near‐horizontal plate interface, but source depths are about 5 km deeper than the established plate interface. The slip directions of the VLF events are slightly (~10°) counterclockwise of the plate convergence direction, indicating that strain energy promoting left‐lateral strike‐slip motion may accumulate in the continental crust during the interseismic period.

show abstract

Determination of focal mechanisms of nonvolcanic tremor using S wave polarization data corrected for the effects of anisotropy

Cited by 15 publications

References 44 publications

Characteristics of slow earthquakes in the very low frequency band: Application to the Cascadia subduction zone

Characteristics of slow earthquakes in the very low frequency band: Application to the Cascadia subduction zone

A new strategy for earthquake focal mechanisms using waveform‐correlation‐derived relative polarities and cluster analysis: Application to the 2014 Long Valley Caldera earthquake swarm

Comparative study of tectonic tremor locations: Characterization of slow earthquakes in Guerrero, Mexico

Contact Info

Product

Resources

About