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Episodic tremor and slip dynamics in south-central Alaska

Baptiste Rousset, Yuning Fu, Noel M. Bartlow, & Roland Bürgmann

Published August 13, 2019, SCEC Contribution #9519, 2019 SCEC Annual Meeting Poster #204

During the last two decades, slow slip events (SSEs) and associated tectonic tremors have been documented downdip of seismogenic zones of young and warm subduction zones. We investigate the relationship between aseismic slip transients and tremors in south-central Alaska, where only independent studies of either process have been carried out so far. Near the eastern downdip edge of the Mw 9.2 1964 Prince Williams earthquake rupture, years-long SSEs have been observed by continuous global positioning system (GPS) measurements. The kinematic modeling of the 2009 - 2013 slow slip event below the upper Cook Inlet suggests transient slip of up to 50 cm, for an equivalent moment magnitude Mw = 7.6. During this 5-year transient event, tremors are co-located with the inferred aseismic slip zone and are happening in weeks-long bursts of events. A clear transient deformation event is observed in GPS time series spanning a tremor burst in September 2010. The time dependent modeling of its slip shows that slip migrates along strike with tremor at speeds of ~ 8 km/day and with slip rates of ~ 3 mm/day. During this Mw 6.9 subevent, 9% of the total moment of the 5-year transient event was released in 1.4% of its duration, showing that slip rates were highly variable during the 5-years transient. To complement the detailed analysis of this single event, we decomposed the GPS time series relative to tremor times during the 5-years transient event. Surface velocities were on average 3 to 6 times higher during tremor bursts than in between, suggesting that slip pulses are always associated with tremor bursts. This inference is strengthened by the decomposition of the GPS time series after the 5-year-long deformation event, when tremor bursts continued to occur. Our results show that short-term slip episodes associated with tremor bursts are occurring during the whole period of overlapping GPS recordings and tremor detections, from 2008 to 2016. Finally, two end-member models could explain the 5-year-long transient deformation event. It could either represent a cluster of short-term events or it could be the sum of short-term ETS events in the tremor zone and a smooth long-term slip event located up dip.

Rousset, B., Fu, Y., Bartlow, N. M., & Bürgmann, R. (2019, 08). Episodic tremor and slip dynamics in south-central Alaska. Poster Presentation at 2019 SCEC Annual Meeting.

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Tectonic Geodesy