Abstract
The Guerrero seismic gap is presumed to be a major source of seismic and tsunami hazard along the Mexican subduction zone. Until recently, there were limited observations at the shallow portion of the plate interface offshore Guerrero, so we deployed instruments there to better characterize the extent of the seismogenic zone. Here we report the discovery of episodic shallow tremors and potential slow slip events in Guerrero offshore. Their distribution, together with that of repeating earthquakes, seismicity, residual gravity and bathymetry, suggest that a portion of the shallow plate interface in the gap undergoes stable slip. This mechanical condition may not only explain the long return period of large earthquakes inside the gap, but also reveals why the rupture from past M < 8 earthquakes on adjacent megathrust segments did not propagate into the gap to result in much larger events. However, dynamic rupture effects could drive one of these nearby earthquakes to break through the entire Guerrero seismic gap.
Highlights
The Guerrero seismic gap is presumed to be a major source of seismic and tsunami hazard along the Mexican subduction zone
It is possible that the silent zone acts as a barrier stopping large earthquakes from becoming much larger and rupturing the NW-Guerrero seismic gap (GG)
Subducting relief interpreted from RG&BAs in the region could have created highly heterogeneous frictional conditions that contribute to generate the conditions for slow slip, such as episodic shallow tremor (ST), possible short-term SSEs repeaters and/or a creeping silent zone
Summary
The Guerrero seismic gap is presumed to be a major source of seismic and tsunami hazard along the Mexican subduction zone. We report the discovery of episodic shallow tremors and potential slow slip events in Guerrero offshore Their distribution, together with that of repeating earthquakes, seismicity, residual gravity and bathymetry, suggest that a portion of the shallow plate interface in the gap undergoes stable slip. Some representative observations of shallow slow earthquakes come from the Japan Trench, where episodic tremor and slip (ETS) preceded the great Tohoku-Oki 2011, Mw 9 earthquake, revealing that slow slip and megathrust earthquakes can coexist at shallow depths of the plate interface[5] For this reason, the near trench portions of subduction zones should be extensively studied to understand the influence of newly subducted materials on its mechanical properties and assess the actual extent of seismogenic zones, which may produce tsunamigenic and devastating earthquakes. Offshore observations show that shallow tremor (ST) is accompanied by SSEs in the weakly coupled shallow plate interface[5,18]
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