The Role of Afterslip and Slow Slip Events in Subduction-Related Earthquake Triggering: The Case Studies of the 2017 M7.1 Mexico City (Puebla) and the 2018 M7.0 Anchorage Earthquakes

Date: 4/24/2019

Time: 05:00 PM

Room: Cascade II

The complex environment of subduction zones offer opportunities to investigate earthquake-to-earthquake interactions. However, examples where non-episodic events may triggered a significant earthquake are sparse. We analyse two cases where ruptures occurred on low-angle normal faults at the hinge of the diving plate; the 2017 M7.1 Puebla earthquake in Mexico, and the 2018 M7.0 Anchorage earthquake in Alaska. We focus on the identification of interaction links incorporating both previous seismic and non-seismic deformation sources. The more landward epicentres of these earthquakes, located above the bending part of the subducting plate, enables the incorporation of extended afterslip and/or slow-slip events (SSEs) recorded by the existing land-based geodetic networks. The 2017 M7.1 Puebla earthquake occurred 11 days after the M=8.1 Chiapas earthquake, setting off public concern about their potential connection. However, no evidence suggests that dynamic triggering or static stress interaction played a role in the nucleation of the second event. The M7.1 Puebla rupture was rooted at the western extension of the afterslip area of the 2012 M7.5 Oaxaca shock that loaded the fault plane by 0.01-0.1 MPa. The 30 November 2018 Anchorage earthquake is the strongest one felt in Alaska since the 1964 M=9.2 Prince William Sound and the 2002 M=7.9 Denali earthquakes. The 1964 coseismic perturbations on the Anchorage plane are estimated >0.5 MPa, though this stress increase occurred more then 54 years ago. We find that recent deformation features of the subduction zone, such as long-lasting slow slip events under Cook Strait exert additional influence. Both recent slow slip episodes the 1992-2004 and 2009-2011 loaded the Anchorage fault plane approximately by 0.1 and 0.05-0.3 MPa, respectively. While the SSEs’ predictive value remains questionable as precursory phenomena to megathrust events, their interaction together with extended postseismic deformation patterns with subduction bending earthquakes requires a closer examination.

Presenting Author: Margarita Segou

Authors