SEISMOLOGICAL EVIDENCE AND DYNAMIC MODELING OF REVERSE RUPTURE PROPAGATION

DURING THE 2010 MW 7.2 EL MAYOR - CUCAPAH EARTHQUAKE

Lingsen Meng, Jean-Paul Ampuero, Morgan Page, Ken Hudnut

Seismo LabCalifornia Institute of Technology

COMPLEXITY OF DYNAMIC RUPTURE

• Complicated rupture patterns emerge in dynamic simulations: variable rupture speed, isolated front, frequency dependent behaviors

• High frequency hard to see in traditional source inversions based on seismic/geodetic observations (<1Hz)

Ripperger, Ampuero, Mai (2008)

2010 EL MAYOR - CUPACAH EARTHQUAKE

(Wei et al,2011)

Eyewitness account byRosario García González,

elder of the Comunidad Cucapah Indígena

(Conducted by Ken Hudnut)

• Shaking before surface rupture

• Reverse rupture direction

(Hutko, 2009)

EARTHQUAKE SOURCE IMAGING BY BACK-

PROJECTION OF ARRAY DATA

2004 Sumatra earthquake (Ishii et al, 2005)

The idea is to stack over different moveouts to recover source locations.

Benefits :No assumptions of prior rupture kinematics and geometry

High frequency aspect of the rupture is complementary to low frequency( finite fault model)

IMAGING EL MAYOR-CUPACAH EVENT BY USARRAY & SIEDCAR ARRAY

• SIEDCAR array at Rio Grande Rift

• Distance 7 ° ~ 12 °• USarray:40 stations• SIEDCAR:60 stations • Oriented 50 ° from

Fault strike• Targeting California

fault systems

• Imaging the strongest asperities• Prominent features repeat in arrivals and codas• Capable of reproducing reverse propagation with realisitic

Green’s function

SYNTHETIC SCENARIOSSlip model with theoretical

Green’s functionReverse rupture with

empirical Green’s function

SEISMOLOGICAL EVIDENCE OF REVERSE RUPTURE

• Bilateral rupture with reverse propagation in the north • Rupture features show up twice as expected from synthetic tests• Result of both arrays are mutually consistent

NWSE

SIMILARITY TO 1984 MORGAN HILL EARTHQUAKE

(Beroza & Spudich,1988)

• directivity effect of phases at different stations

• A asperity first resisted to fail, but eventually ruptured inward and slip massively

1. Dynamic triggering of detached asperity2. Later break of shallower barrier

NWSE

DYNAMIC RUPTURE MODELS

Yiel

d st

ress

Slip

vel

ocity

Accu

mul

ated

slip

(Dynamic simulation conducted by Morgan Page)

SHALLOW BARRIER FROM GEOMETRICAL FAULT COMPLEXITY

(Fletcher et al)

Flower structures in strike slip tectonics

SUMMARY

NWSE

• Reverse rupture supported from both eye witness account and regional seismic back projection.

• Later break of shallow barrier (geometrical complexity) is a dynamically plausible interpretation