Abstract: Tectonic Tremor observations in Guerrero, Mexico and how SSE strain field modeling including pore fluid evolution explain the observations (2015 Joint Assembly)

Tectonic Tremor observations in Guerrero, Mexico and how SSE strain field modeling including pore fluid evolution explain the observations

Allen L Husker¹, William Benjamin Frank², Victor M Cruz-Atienza³, Vladimir Kostoglodov¹, Nikolai Shapiro⁴, Carlos Villafuerte⁵ and Emmanuel Caballero¹, (1)UNAM National Autonomous University of Mexico, Mexico City, Mexico, (2)Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, Cambridge, MA, United States, (3)Universidad Nacional Autonoma de Mexico, Mexico City, Mexico, (4)Institut de Physique du Globe de Paris, Paris, France, (5)Ecole Normale Supérieure Paris, Laboratoire de Géologie, Paris, France

Contact First Author: Allen L Husker; ahusker@caltech.edu

Previously Published Material: The observations have been partly published in the following publication: Frank, W., N. Shapiro, A. Husker, V. Kostoglodov, A. Romanenko, M. Campillo (2014), Using systematically characterized low-frequency earthquakes as a fault probe in Guerrero, Mexico, J. Geophys. Res., 119, 7686–7700, doi:10.1029/ 2014JB011457.The modeling will be presented in the SSA meeting in April.This presentation in Montreal will be the first of the two together.

Abstract ID#: 35096

English Abstract:

Tectonic tremor (TT) in Mexico has a complicated behavior. All tremors occur close to the plate interface near 40 km depth. The area of TT activity is divided into 3 zones. The transient zone located ~130 km – 165 km from the trench. The buffer zone, which has very little TT and is located ~165 km – 190 km from the trench. The Sweet Spot (~190 km – 245 km) has the overwhelming majority of TT. Previous studies have shown near continuous TT within the Sweet Spot with large bursts of activity about 3 - 5 times a year. Low frequency earthquake (LFE) studies show that during a burst LFE streaks are seen in the Sweet Spot that travel trench perpendicular (10’s km/hr). After several days LFE’s are found within the transient zone, however they do not appear to streak or be related to the streaks in the other zones. These bursts correlate with small slip seen on the GPS record and are considered small, short-term slow slip events (small SSE). The Sweet Spot also has a near continuous amount of smaller bursts that do not streak, do not cross into the buffer zone and do not provoke LFE’s in the transient zone. The large, long-term slow slip events (SSE) that occur approximately every 4 years in Guerrero provoke a very large number of TT bursts. The LFE’s farthest from the trench show no difference in their rate during the majority of the SSE. The closer the LFE’s are to the trench the more they are found to occur in separate bursts, which suggests that they are more "stick-slipy". In the last stage of the SSE, the number of LFE’s declines dramatically with the greater the decline the further the distance from the trench. Poroelastic modeling of fluid transport during the large SSE shows that fluid migrate toward the Sweet Spot with maximum velocities of ~10^-3 km/day, which is more than 3 orders of magnitude slower than all of the LFE/TT migration speeds mentioned above suggesting that fluid transport cannot explain these observations. However, Coulomb Failure Stresses due to the SSE strain field including pore pressure evolution (through the effective stresses) are consistent with the time-dependent occurrence frequency of LFEs during the large SSE. A small SSE strain field could potentially produce the smaller SSE/TT episode observations that fluid migration cannot explain due to the wildly varying TT time scales and velocities.

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