Videos of quakes 5.5 available for downloading 1.5 hours after occurrence
is known about the subsurface structure of the region. The shape of underground geological structures in the area not recorded on seismograms is key, Tromp said, as the structures can greatly affect wave motion by bending, speeding, slowing or simply reflecting energy. The simulations are created on a parallel processing computer cluster built and maintained by PICSciE and on a computer cluster located at the San Diego Supercomputing Center.
After the three-dimensional simulations are computed, the software program plugs in data capturing surface motion, including displacement, velocity and acceleration, and maps it onto the topography of the region around the earthquake. The movies then are automatically published via the ShakeMovie portal. An e-mail also is sent to subscribers, including researchers, news media and the public.
The simulations will be made available to scientists through the data management center of the Incorporated Research Institutions for Seismology (IRIS) in Seattle. The organization distributes global scientific data to the seismological community via the Internet. Scientists can visit the IRIS Web site and download information. Due to the research team’s work, they now will be able to compare seismograms directly with synthetic versions.
Advanced computing power made the synthetic seismograms possible, according to Dennis McRitchie, another author on the paper and a lead high-performance computing analyst for Princeton’s Office of Information Technology. “This is computationally intensive — it takes five hours to produce a 100-minute simulation,” McRitchie said. The effort to numerically solve the differential equations that govern how the waves propagate through these complicated earth models requires 384 computers operating in parallel to analyze and process the numbers.
When an earthquake occurs, seismic waves are generated that propagate away from the fault rupture and course along the Earth’s surface. The videos show the up-and-down motion of the waves in red (up) and blue (down). Strong red waves indicate rapid upward motion. Strong blue waves indicate the Earth’s surface is moving quickly downward. The simulation shows that the waves are of uneven strength in different areas, depending on the quality of the soil and the orientation of the earthquake fault. When the waves pass through soft, sedimentary soils, they slow down and gain strength. Waves speed up through hard rock, lessening the impact on surface areas above. A clock in the video shows the time since the earthquake occurred.
The ShakeMovie portal showing earthquakes around the world is similar to one maintained at the California Institute of Technology that routinely does simulations of seismic events in the Southern California region.
Earthquake movies will be available for download about 1.5 hours after the occurrence of a quake of magnitude 5.5 or greater.
The research was funded by the National Science Foundation.
