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(a)20121028 M7.7 Dist: 2080.0 km BAZ: 337.7 deg Station: BK.PKD

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Tectonic Tremor Triggered along Major Strike-Slip Faults around the World Chastity Aiken1, Zhigang Peng1, David R. Shelly2, David P. Hill2, Hector Gonzalez-Huizar3, Kevin Chao4, Jessica Zimmerman5, Roby Douilly6, Anne Deschamps7, Jennifer Haase8, and Eric Calais9

1Georgia Institute of Technology; 2 U.S. Geological Survey, Menlo Park; 3 University of Texas, El Paso; 4 University of Tokyo, Earthquake Research Institute; 5 Texas A & M University, Commerce; 6 Purdue University; 7 Université de Nice Sophia Antipolis; 8 Scripps Institute of Oceanography; 9 Ecole Normale Superieure

Research Question How does triggered tremor differ on strike-slip faults around the world?

Methods  Select a study region

Select earthquakes as potential triggers

Retrieve, process, and analyze seismic data

Strike-slip faults with no tremor observations, comparable to the San Andreas Fault

Shallow, less < 100 km depth Magnitude > 5.5 Distance > 100 km Peak dynamic stress > 1 kPa

Instrument correction Filtering Triggered tremor identification Triggered tremor location

Figure 2. Location of tremor sources around the world, with regions where tremor has not previously been discovered (this study) marked as red stars.

Figure 1. Illustration of the brittle, fast-slipping seismogenic zone (red), and slow-slip zones (yellow), and stable sliding zones (blue) for a vertical fault. Red zone is where earthquakes generally occur. Tremor generally occurs in the region marked by the ellipse. From Kanamori (2008).

Background Deep tectonic tremor, which generally occurs in the lower crust beneath the seismogenic zone where earthquakes occur, has been observed at several major plate-bounding faults around the Pacific Rim. In order to investigate the potential link between tremor and earthquake nucleation, further study of when, where, and how tremor occurs is needed. Tremor is known to occur ambiently, sometimes in association with GPS detected slow-slip events but could also be triggered by small stress perturbations arising from solid earth tides as well as passing seismic waves of a distant earthquake. Because triggered tremor occurs on the same fault patch as ambient tremor (Gomberg, 2010) and generally has a higher signal-to-noise ratio, it is relatively easy to identify. We present a review of triggered tremor in 4 strike-slip regions: (1) the Eastern Denali Fault in Yukon, Canada, (2) the Queen Charlotte Fault near Haida Gwaii, Canada, (3) the San Andreas Fault near Parkfield, CA, and (4) the Enriquillo-Plaintain Garden Fault in the southern Haiti peninsula. We characterize triggered tremor as broadband signals with long duration that are coincident with surface waves from a distant earthquake. We locate tremor sources using the envelope cross-correlation method or a matched filter technique (Shelly et al., 2006) if it is visible on 3 or more stations. We discuss triggering potential in each region in terms of dynamic stress, seismic wave incidence, and frequency dependence.

Triggered Tremor Observations

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Queen Charlotte Fault of Haida Gwaii, Canada

134˚W 132˚W 130˚W

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PlatePacificPlate

Juan de FucaPlate

Figure 4. Tremor triggered near the Queen Charlotte Fault of western Canada. From Aiken et al. (2013). (LEFT) Map view of the Queen Charlotte Fault with average triggered tremor sources marked by circles. Stations are triangles. Stars and dots are earthquakes. (RIGHT) Example of tremor triggered by the 2011/03/11 Mw9.0 Tohoku-Oki, Japan earthquake.

Eastern Denali Fault of Yukon Territory, Canada

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Figure 3. Tremor triggered near the Eastern Denali Fault of northwest Canada. (LEFT) Map view of the Eastern Denali Fault with average triggered tremor sources marked by circles. Stations are triangles. “Beach balls” and dots are earthquakes. (RIGHT) Example of tremor triggered by the 2013/01/05 Mw 7.5 Craig, AK earthquake (green star in map above).

-148˚ -146˚ -144˚ -142˚ -140˚ -138˚ -136˚60˚

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San Andreas Fault of Parkfield, California

Figure 5. Tremor triggered on the San Andreas Fault near Parkfield, CA. (LEFT) Map view of the San Andreas Fault with average triggered low-frequency earthquake (LFE) sources marked. Dots are earthquakes. (RIGHT) Example of tremor triggered by the 2012/10/28 Mw 7.7 Haida Gwaii earthquake. Red circles are matched filter detected LFEs (Shelly et al. 2006).

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(a)20100227 M8.8 Dist: 5985.8 km BAZ: 180.2 deg Station: CN.JAKH

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Enriquillo-Plantain Garden Fault of Haiti

73.5˚W 73˚W 72.5˚W 72˚W

18˚N

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73.5˚W 73˚W 72.5˚W 72˚W

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EPGF 6 +/- 2 mm yr-1

Figure 6. Tremor triggered near the Enriquillo-Plantain Garden (EPG) Fault of the southern Haiti peninsula. (LEFT) Map view of the EPG Fault with triggered tremor bursts marked by circles (average location marked by green star). Land stations are triangles. OBS stations are marked by their names. White star and dots are Haiti mainshock and its aftershocks. (RIGHT) Example of tremor triggered by the 2010/02/27 Mw8.8 Maule, Chile earthquake.

Conclusions •  We discovered triggered tremor on 3 strike-slip faults where tremor was not

previously reported.

•  We located the tremor sources to be on or near the fault traces in each of the regions. •  Our triggering observations are in agreement with the Coulomb failure criterion (Hill

and Prejean, 2013).

•  Long period, large amplitude surface waves are responsible for triggering tremor in these regions, as has been observed elsewhere.

•  The Parkfield segment of the San Andreas Fault is more easily triggered than the other regions, which reflects recent strength properties of the fault.

C.A. is supported by National Science Foundation (NSF) Graduate Research Fellowship DGE-1148903. Z.P. is supported by NSF CAREER grant EAR-0956051.

Literature Cited  Aiken, C., Z. Peng, and K. Chao (2013), Tremor triggered along the Queen Charlotte Margin by large teleseismic earthquakes, Geophys. Res. Lett., 40, doi: 10.1002/grl.50220. Gomberg, J. (2010), Lessons from (triggered) tremor, J. Geophys. Res., 115(B10), doi: 10.1029/2009JB007011. Hill, D. P. and S. Prejean (2013), Dynamic triggering, vol. 4, Earthquake Seismology, Treatise on Geophysics. Kanamori, H. (2008), Earthquake physics and real-time seismology, Nature, 451, 271-273, doi:10.1038/nature06585. Shelly, D. R., G. C. Beroza, S. Ide, and S. Nakamula (2006), Low-frequency earthquakes in Shikoku, Japan, and their relationship to episodic tremor and slip, Nature, 442, 188-191, doi: 10.1038/nature04931.

Acknowledgments  

Triggering Potential

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2011 Tohoku−Oki2012 Sumatra2012 Haida Gwaii2013 Craig, Alaska

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2002 Denali2004 Sumatra2010 Chile2011 Tohoku−Oki2012 Sumatra

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Eastern Denali Fault

Queen Charlotte Fault

Enriquillo-Plantain Garden Fault

Figure 8 (RIGHT). Triggering earthquake characteristics for all earthquakes studied in Yukon, Canada. (a) Peak transverse dynamic stress vs. angle of seismic wave incidence. (b) Surface wave velocity spectra. Event labels in (b) also pertain to outline color in (a) and in map for this region (Figure 3).

Figure 9 (LEFT). Triggering earthquake characteristics for all earthquakes studied in Haida Gwaii, Canada. Symbols and notation are the same as in Figure 7. Event labels in (b) also pertain to outline color in (a) and in map for this region (Figure 4).

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by H. Gonzalez-Huizar (2013)UTEP

NVT in Haiti triggered by the 2010 Mw8.8 Maule, Chile earthquake

Figure 11 (LEFT). Time dependent dynamic stress computed for the Enriquillo-Plantain Garden Fault at 20 km depth with a friction coefficient of 0.2. (TOP) Vertical and transverse displacement seismogram. (MIDDLE) Dynamic “stress”grams for vertical and transverse components. (BOTTOM) Tremor and envelope.

Figure 7 (LEFT). Theoretical example of triggering potential as a function of wave amplitude (i.e. stress), depth (i.e. frequency), and incidence angle on a vertical strike-slip fault. From Hill and Prejean (2013).

Corresponding Author: chastity.aiken@gatech.edu

San Andreas Fault

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121.5˚W 121˚W 120.5˚W 120˚W

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Seismic Stations

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S51B-2362