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Dynamic Rupture Simulations on the Alpine Fault: Investigating the Role of Fault Geometry on Rupture Size and Behavior

Description: 

The right-lateral transpressional Alpine Fault is the primary plate boundary fault on the South Island of New Zealand. At a broad scale, its onshore surface trace between Milford Sound in the southwest, and the branching Marlborough Fault System in the northeast consists of two planar sections connected by a major geometrical boundary at Martyr River. This boundary is characterized by both a dip change of as much as 40° over an along-strike length of only ~5 km (e.g., Warren-Smith et al. [2022]) and by two small (8–13 km) subparallel strands near a ~6° restraining bend. Several previous studies suggest that changes in dip along a strike-slip fault (e.g., Lozos [2021]) as well as smaller fault features can both affect rupture dynamics (e.g., Lozos et al. [2012]); we therefore hypothesize that these geometrical features affect conditional earthquake segmentation behavior on the Alpine Fault, as documented by the extensive paleoseismic record (e.g., Howarth et al. [2001]).

We use the 3D finite element method to simulate dynamic ruptures on four idealized parameterizations of the onshore Alpine Fault geometry: 1. a single vertical plane, 2. a vertical plane with two smaller parallel vertical planes at the restraining bend, 3. a single dipping plane, and 4. a dipping plane with two smaller dipping planes at the bend. We embed the faults in a 1D velocity structure and impose heterogeneous initial tractions computed using seismologically estimated local principal stress orientations and magnitudes computed using a critically-stressed crust model. We compare the modelled rupture lengths and surface slip values to geologic and paleoseismic studies to ensure that we are producing physically-plausible simulations consistent with observations. These simulations may be helpful not only in assessing the hazard associated with the Alpine Fault, but also in constraining the geometry of the fault and implications for rupture directivity.

Session: Opportunities and Challenges in Source Modeling for Seismic Hazard Analysis

Type: Oral

Date: 4/20/2023

Presentation Time: 09:00 AM (local time)

Presenting Author: Julian Lozos

Student Presenter: No

Invited Presentation: 

Authors