Triggered tremor sweet spots in Alaska

Abstract

To better understand what controls fault slip along plate boundaries, we have exploited the abundance of seismic and geodetic data available from the richly varied tectonic environments composing Alaska. A search for tremor triggered by 11 large earthquakes throughout all of seismically monitored Alaska reveals two tremor “sweet spots”—regions where large‐amplitude seismic waves repeatedly triggered tremor between 2006 and 2012. The two sweet spots locate in very different tectonic environments—one just trenchward and between the Aleutian islands of Unalaska and Akutan and the other in central mainland Alaska. The Unalaska/Akutan spot corroborates previous evidence that the region is ripe for tremor, perhaps because it is located where plate‐interface frictional properties transition between stick‐slip and stably sliding in both the dip direction and laterally. The mainland sweet spot coincides with a region of complex and uncertain plate interactions, and where no slow slip events or major crustal faults have been noted previously. Analyses showed that larger triggering wave amplitudes, and perhaps lower frequencies (<~0.03 Hz), may enhance the probability of triggering tremor. However, neither the maximum amplitude in the time domain or in a particular frequency band, nor the geometric relationship of the wavefield to the tremor source faults alone ensures a high probability of triggering. Triggered tremor at the two sweet spots also does not occur during slow slip events visually detectable in GPS data, although slow slip below the detection threshold may have facilitated tremor triggering.

Delayed dynamic triggering: Local seismicity leading up to three remote M ≥ 6 aftershocks of the 11 April 2012 M8.6 Indian Ocean earthquake

“…The 16 M ≥ 5.5 triggered earthquakes reported by Pollitz et al [2012] all occur more than 14 h after the IOE, suggesting a failure process must exist that is more complex than Coulomb failure for these larger events [Hill, 2015]. Journal of Geophysical Research: Solid Earth 10.1002/2015JB012243 Gomberg and Prejean, 2013;Linville et al, 2014;Tape et al, 2013]. However, the data resolution in our study areas is not applicable to resolving triggered tremor.…”

“…The 16 M ≥ 5.5 triggered earthquakes reported by Pollitz et al [] all occur more than 14 h after the IOE, suggesting a failure process must exist that is more complex than Coulomb failure for these larger events [ Hill , ]. The IOE did immediately trigger remote tremor and low‐magnitude earthquakes ( M < 4) during the surface wave passage [ Aiken et al , , ; Chao and Obara , ; Fuchs et al , ; Gomberg and Prejean , ; Linville et al , ; Tape et al , ]. However, the data resolution in our study areas is not applicable to resolving triggered tremor.…”

Triggered Seismic Events along the Eastern Denali Fault in Northwest Canada Following the 2012 Mw 7.8 Haida Gwaii, 2013 Mw 7.5 Craig, and Two Mw>8.5 Teleseismic Earthquakes

“…1). Recent studies have detected ambient and triggered tremor in south-central mainland Alaska (Peterson and Christenson, 2009;Gomberg and Prejean, 2013). The tremor discovered in those studies lie where the Yakutat terrane is transitioning from flat-slab subduction in the west to a zone of collision in the east, resulting in a fold-and-thrust belt (Worthington et al, 2012).…”

“…We searched for tremor on stations surrounding the central Denali fault, and the triggered tremor generally arrives at station KLU prior to PAX (e.g., Ⓔ Fig. S10), suggesting that they mostly occur further south in the south-central Alaska sweet spot Gomberg and Prejean, 2013). No tremor signal was observed on station DDM (seismic data archived for only 1 yr, from [2009][2010], located north of the central Denali fault.…”

Near‐continuous tremor and low‐frequency earthquake activities in the Alaska‐Aleutian subduction zone revealed by a mini seismic array

“…In the last 80 years, four large earthquakes with M w > 8 have occurred: the 1938 M w 8.2 Shumagin Islands, 1957 M w 8.6 Andreanof Islands, 1964 M w 9.2 Good Friday, and 1965 M w 8.7 Rat Islands earthquakes [ Brown et al , ] (Figure ). TT and LFEs have previously been identified in south central Alaska and along the Alaska‐Aleutian Arc [ Brown et al , ; Gomberg and Prejean , ; Peterson et al , ]. Details of their spatiotemporal distribution, however, is poorly known due to limited number of tremor/LFE studies in this area.…”