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Constraints on Crustal Stress in South Island, New Zealand from Coseismic Slip Models of the 2016 Kaikoura, 2010 Darfield and 2011 Christchurch Earthquakes

Session: Crustal Stress and Strain and Implications for Fault Interaction and Slip [Poster]

Type: Poster

Date: 4/22/2021

Presentation Time: 11:30 AM Pacific

Description: 

We estimate the tensorial seismogenic stresses that led to the 2016 M_w7.8 Kaikoura, 2010 M_w7.1 Darfield, and 2011 M_w6.3 Christchurch earthquakes, using published geodetically and seismically derived coseismic slip models. We estimate the orientations of the principal stresses and the relative magnitudes of the least and intermediate compressive stresses relative to the most compressive stresses (MCS; the MCS magnitude cannot be constrained from coseismic slip data). Our estimation of stress relies on the Wallace-Bott assumption, which posits that when a fault slips, it does so in the direction in which it was loaded, and thus our estimated stresses are those prior to the individual earthquakes. We consider eleven coseismic slip models, seven of the Kaikoura earthquake, and two each of the Darfield and Christchurch earthquakes. We estimate the stress using a Markov Chain Monte Carlo strategy. For all of the earthquakes, we find that the relative magnitudes of the principal stresses are poorly constrained, and that each of the coseismic slip models are individually consistent with a single stress state, despite the complexity in some of the slip models. There are noticeable differences in the stress orientations estimated from the coseismic slip models of the three earthquakes, although most of the models indicate a roughly EW trending, sub-horizontal to shallowly plunging MCS direction. Preliminary results indicate significant changes in stress from the Kaikoura earthquake to the two earthquakes to the south. The least compressive stress (LCS) direction estimated from the Kaikoura coseismic slip models is near vertical, while LCS is estimated to be sub-horizontal from the Darfield and Christchurch earthquakes, indicating a transition from a thrust-like to a strike-slip stress regime from north to south along the east coast of South Island, New Zealand.

Presenting Author: Olivia L. Helprin

Student Presenter: Yes

Authors