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Plourde et al. (2015)

Low-frequency earthquakes at the southern Cascadia margin

A. P. Plourde, M. G. Bostock, P. Audet, and A. M. Thomas

DOI

(top) LFE families are plotted in plan view along with earthquakes and the 20, 30, 40, and 50 km depth contours from the McCrory et al. [2012] plate interface model. Each LFE family is labeled with its depth in kilometers. The southern LFE families at 15 km and 21 km depth lie on the Maacama Fault, while the family at 16 km depth lies on Bucknell Creek Fault. The location of the two shallow earthquakes used as templates for network cross correlation is indicated with blue circles. MTJ: Mendocino Triple Junction, SAF: San Andreas Fault, MF: Maacama Fault, BCF: Bucknell Creek Fault, BSF: Bartlett Springs Fault.

Figure 1:(top) LFE families are plotted in plan view along with earthquakes and the 20, 30, 40, and 50 km depth contours from the McCrory et al. [2012] plate interface model. Each LFE family is labeled with its depth in kilometers. The southern LFE families at 15 km and 21 km depth lie on the Maacama Fault, while the family at 16 km depth lies on Bucknell Creek Fault. The location of the two shallow earthquakes used as templates for network cross correlation is indicated with blue circles. MTJ: Mendocino Triple Junction, SAF: San Andreas Fault, MF: Maacama Fault, BCF: Bucknell Creek Fault, BSF: Bartlett Springs Fault.

Summary

We use seismic waveform data from the Mendocino Experiment to detect low-frequency earthquakes (LFEs) beneath Northern California during the April 2008 tremor-and-slip episode. In southern Cascadia, 59 templates were generated using iterative network cross correlation and stacking and grouped into 34 distinct LFE families. The main front of tremor epicenters migrates along strike at 9 km d−1; we also find one instance of rapid tremor reversal, observed to propagate in the opposite direction at 10–20 km h−1. As in other regions of Cascadia, LFE hypocenters from this study lie several kilometers above a recent plate interface model. South of Cascadia, LFEs were discovered on the Maacama and Bucknell Creek faults. The Bucknell Creek Fault may be the youngest fault yet observed to host LFEs. These fault zones also host shallow earthquake swarms with repeating events that are distinct from LFEs in their spectral and recurrence characteristics.

Catalog Summary

Notes

Unfortunately this dataset does not contain detection times for all templates in the study, as some were lost to a corrupted hard drive. Times for a given template are detection times and not origin times. The detection time is offset from the origin time by less than one minute.

References
  1. Plourde, A. P., Bostock, M. G., Audet, P., & Thomas, A. M. (2015). Low‐frequency earthquakes at the southern Cascadia margin. Geophysical Research Letters, 42(12), 4849–4855. 10.1002/2015gl064363
  2. Verdonck, D., & Zandt, G. (1994). Three‐dimensional crustal structure of the Mendocino Triple Junction region from local earthquake travel times. Journal of Geophysical Research: Solid Earth, 99(B12), 23843–23858. 10.1029/94jb01238
Catalogs
Bostock et al. (2015)
Catalogs
Stone et al. (2018)