The strength inversion origin of non-volcanic tremor: observations and models
Abstract
Non-volcanic tremor is the least understood form of seismic activity. In its most common subduction zone setting, tremor typically occurs within the plate interface at or near the shallow and deep edges of the interseismically locked zone. Detailed seismic observations have shown that tremor is composed of repeating small low-frequency earthquakes (LFE), often accompanied by very-low-frequency earthquakes (VLF), all involving shear failure and slip. However, LFEs and VLFs within each cluster show nearly constant source durations for all observed magnitudes, which implies asperities of near-constant size. Here we integrate geological observations and geomechanical lab measurements on heterogeneous rock assemblages representative of the shallow tremor region with numerical simulations to demonstrate that LFEs and VLFs are consistent with the seismic failure of relatively weaker blocks within a stronger matrix. Furthermore, in these shallow subducting rocks hydrothermal fluids have led to a strength-inversion from a weak matrix with relatively stronger blocks to a stronger matrix with embedded relatively weaker blocks. In this case, tremor naturally occurs as the now-weaker blocks fail seismically while their more competent surrounding matrix has not yet reached a state of general seismic failure, and instead only fails at local stress-concentrations around the tremorgenic blocks. We illustrate this with a suite of numerical experiments that explore this evolution of deformation and stress in a subduction channel and its implications for slow-slip and seismogenesis. This mechanism directly explains shallow tectonic tremor that clusters in spatially discontinuous swarms along the plate interface. At the deeper edge of the interseismically locked zone, channelised dehydration associated with subduction along a plate interface could induce a similar relative strength inversion, and thereby generate deep seated tremor.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.T52A..05V
- Keywords:
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- 1242 Seismic cycle related deformations;
- GEODESY AND GRAVITY;
- 7223 Earthquake interaction;
- forecasting;
- and prediction;
- SEISMOLOGY;
- 8118 Dynamics and mechanics of faulting;
- TECTONOPHYSICS;
- 8163 Rheology and friction of fault zones;
- TECTONOPHYSICS