SCEC Award Number 16173 View PDF
Proposal Category Individual Proposal (Integration and Theory)
Proposal Title Strike-slip Faulting Energy Release and Supershear Rupture
Investigator(s)
Name Organization
Jean-Philippe Avouac California Institute of Technology
Other Participants Lingling Ye, Postdoctoral Scholar
SCEC Priorities 4a, 4b, 4d SCEC Groups FARM
Report Due Date 03/15/2017 Date Report Submitted 05/09/2017
Project Abstract
 Given that large strike-slip earthquakes are a major concern for Southern California, improved empirical understanding of radiated energy from this class of events is desirable both for evaluating seismic ground motion. We had a focused effort on the 2016 Mw 7.8 Kaikoura, New Zealand earthquake combining remote sensing observations, back projection of the high-frequency teleseismic seismic waves and finite source modeling of teleseismic waveforms. We also analyzed globally distributed dataset of large megathrust and strike-slip events to determine empirical laws which should help anticipate seismic radiation and ground shaking from future large events in California. We defined a new metrics, the radiated energy enhancement factor (REEF), defined by the ratio of the directly measured broadband radiated energy to the calculated minimum radiated energy for an event with the same seismic moment and duration. We show that this metrics quantifies the complexity of earthquake ruptures and show striking systematic regional correlations that suggesting that the complexity of megathrust earthquake ruptures is strongly influenced by persistent geological factors. Two publications were prepared, one has now been published. Presentations were given at the SCEC annual meeting and AGU Fall meeting.
Intellectual Merit California is exposed produces a risk of very large strike-slip earthquakes like the 1906 San Francisco and 1857 Fort Tejon earthquakes. Only a few, significantly smaller, strike-slip events have occurred recently in California for which modern instrumental recordings are available. There is therefore much to learn from studying modern equivalent events in other regions, such as the Mw7.8 Kaikoura earthquake. We analyzed this particular event in some detail using modern remote sensing and seismological techniques. We also conducted a global analysis of recent very large strike-slip ruptures.
Broader Impacts The project provided partial support for a promising young, Asian woman scientist , Ms. Lingling Ye’s who took a postdoctoral position at Caltech in Fall 2015.

The PI was interviewed by Science magazine regarding the learning from the Kaikoura earthquake: Science Magazine-Mar 23, 2017, http://www.sciencemag.org/news/2017/03/strange-behavior-new-zealand-quake-suggests-higher-chances-big-ones-elsewhere.
The implications of what was learned from studies of the Kaikoura and Gorkha earthquakes for California earthquakes are discussed on the web at :
- http://temblor.net/earthquake-insights/could-several-california-faults-rupture-together-as-in-the-m7-8-new-zealand-earthquake-2981/
- http://temblor.net/earthquake-insights/mw7-8-earthquake-shakes-new-zealand-causes-tsunami-1762/
Exemplary Figure Figure 1. Model of the Kaikoura earthquake derived from the surface deformation and teleseismic waveforms (Hollingsworth et al, 2017). The model considers one shallow dipping thrust fault (E1) and shallower strike-slip fault (E2) that reaches the surface along the Kekerengu and Jordan faults. (a) Coseismic slip distribution on the fault E1 along with the corresponding moment tensor solution (red beach ball). The red and blue stars are the initiations for rupture on the faults E1 and E2 respectively. Circles colored for depth show aftershock and mainshock epicenters from the GNS catalogue. (b) Coseismic slip distribution on fault E2 along with the corresponding moment tensor solution (blue). Inset show the moment rate as function of time from only source E2 (red), only E1 (black) and E1 +E2 (gray). Other symbols are same as (a). (c) Black vectors show horizontal surface displacements predicted by our slip model. The color coding shows amplitude of eastward component. Blue arrows show coseismic horizontal displacements measured from GPS. (d) Vectors show horizontal surface displacements predicted by our source model. The color coding shows amplitude of vertical surface deformation.