The latest advances in computing now allow for 3D simulation of wave propagation; techniques simply not available to us previously. This will allow us to better understand the rupture and resulting ground motions of the largest earthquakes in greater detail. How can this new method be used to better assess earthquake impact?
Seismologists predict that it is very likely that California will experience an earthquake measuring 6.7 on the Richter scale during the next 30 years. An even larger quake – of 7.0 magnitude – is 94% certain. But even those mighty temblors would pale next to “the big one,” the moniker for a magnitude 7.5 or greater quake on the San Andreas Fault.
San Diego State University professor and seismologist Kim Olsen and colleagues have created a computer-generated model of this monster quake in order to project its capacity for destruction.
Ground motion and shaking in a 3D world
Recent large-scale 3D modeling exercises using physics-based simulations have provided useful insight into the factors that control the ground-motion levels for large earthquakes. These help determine the amount of shaking that could occur in an area.
Path effects can amplify the ground motions significantly, demanding high accuracy of the underlying crustal model. For example, wave-guide channeling effects can generate 10-fold differences in long-period peak ground motions dependent on the epicentral location.
The strong localized amplification effects from the wave guide are highly sensitive to the details of the 3D velocity model used in the simulations. Counteracting these amplification mechanisms, nonlinear effects can significantly reduce peak ground motions for large scenario earthquakes.
Smaller-scale heterogeneities generating scattering in the crustal structure are modeled statistically to reach the higher frequency signals required by structural engineers for smaller structures.
The 3D modeling of ground motions is a computationally extensive technique that can be used to improve seismic hazard maps using work flows and high-performance computing. The CyberShake project through the Southern California Earthquake Center (SCEC) is designed to generate probabilistic seismic hazard analysis (PSHA) curves using hundreds of thousands of rupture variations on contributing faults and a 3D model of the subsurface.
As a keynote speaker at the next WRN seminar on seismic risk, Kim will review the results of the 3D CyberShake project, and evaluate the benefits compared to conventional, empirically-based PSHA, and how the results may be used in next-generation hazard maps.
During the upcoming WRN seminar on seismic risk, professor Olsen, an internationally renowned expert on this pioneering technique, will present lessons learned from earthquake scenarios that would affect tens of millions of people:
- M7.7+ strike-slip events on the southern San Andreas fault
- M7.0 normal fault scenarios on the Wasatch fault, Utah,
- M9.0 megathrust events in the Cascadia subduction zone in the Pacific Northwest of the USA.
If you want to learn more about this, join us for an afternoon of cutting edge earthquake science discussions at our upcoming WRN Seminar on Seismic Risk, on February 23rd.
Kim Olsen is a professor at the Department of Geological Sciences of San Diego State University. His research interests include 3-D simulation of wave propagation using finite differences, strong ground motion and site amplification, earthquake dynamics, non-linear effects in strong ground motion, and parallel and high-performance computing. He has been involved in projects such as broadband simulation of ground motion from large earthquakes; 3-D modelling of strong ground motion from M 7.0 earthquakes on the Salt Lake City Segment of the Wasatch Fault, Utah; forward and inverse modelling of rupture dynamics in three dimensions; and verification and validation of numerical simulation methods.