Imaging the distribution of transient viscosity after the 2016 Mw 7.1 Kumamoto earthquake

Crustal rock strength from outer space The response of crustal rock to stresses is challenging to estimate yet vital for determining risks from events such as earthquakes. Moore et al. take advantage of the recent Mw 7.1 Kumamoto earthquake in Japan to determine the rheology of crustal rocks in the region. The observed inversion of the crustal strain rates demonstrates that certain areas have stiff rock and others (e.g., under the Aso volcanic complex) have much weaker rock. The results match up with expectations, which means that the method can successfully measure rock properties over a wide range of strength and large spatial and temporal scales. Science, this issue p. 163 The combination of GPS and InSAR data after the Kumamoto earthquake in Japan allows for an estimate of regional rock rheology. The deformation of mantle and crustal rocks in response to stress plays a crucial role in the distribution of seismic and volcanic hazards, controlling tectonic processes ranging from continental drift to earthquake triggering. However, the spatial variation of these dynamic properties is poorly understood as they are difficult to measure. We exploited the large stress perturbation incurred by the 2016 earthquake sequence in Kumamoto, Japan, to directly image localized and distributed deformation. The earthquakes illuminated distinct regions of low effective viscosity in the lower crust, notably beneath the Mount Aso and Mount Kuju volcanoes, surrounded by larger-scale variations of viscosity across the back-arc. This study demonstrates a new potential for geodesy to directly probe rock rheology in situ across many spatial and temporal scales.

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