Seismic Mini-Arrays for the NVT study

Seismic mini-arrays for the NVT study in Mexico

There is a growing scientific challenge to understand the origin of recently discovered Slow Slip Events (SSE) and Non-Volcanic Tremor (NVT). SSE and NVT observed now in different subduction zones (Japan, Alaska, Cascadia, Mexico, Costa Rica, New Zealand) may be a very important constituent in the seismic cycle of large subduction thrust earthquakes. According to one hypothesis, the SSE which occurs on the plate interface down dip of the seismogenic zone can slightly increase the shear stress on this coupled segment and trigger a rupture of the mature seismic gap.
Large number of observations show that the SSE is usually associated with an increased NVT activity but it is not clear yet if the NVT and SSE represent the same seismotectonic phenomenon or those are independent expressions of a common origin. Up to day there has been no detection of any reliable case of triggering of large subduction thrust events by the SSE. Nevertheless, GPS and Long Baseline Tiltmeter data showed that the 2001-2002 SSE in Guerrero has probably incited two M ~ 6 seismic events: one of the normal focal mechanism, crustal event in the coastal zone of Guerrero in 2001 (right after the SSE commence) and another tsunamigenic thrust earthquake close to the Middle America Trench at the end of this SSE.
Sometimes relatively large NVT bursts occur during “quiet” epochs when the SSE is not happening or does not achieve a sufficient magnitude to be recorded with available instruments. The NVT activity episodes are easier to record than small magnitudes SSE, and thus can be considered a very important monitoring tool.

Seismic mini-array (TOMA) installed in Tomatal, Guerrero. A lot of NVT bursts are occurring in this area. The most problematic task is depth estimates of the NVT. According to preliminary results based on the MASE seismic data, the NVT are happening here at the depths from 10 to 45 km. The more precise localization and depth assessments of the NVT are expected to obtain from the network of seismic mini-arrays deployed around the NVT clustering zone.