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NEWSWISE — The Hayward fault, part of the larger San Andreas fault system, runs 74 miles through the East Bay of the San Francisco Bay Area. The fault is overdue for an earthquake that could cause extensive damage to such a dense population zone.

In a recent study, published in , scientists at Lawrence Livermore National Laboratory (LLNL) and Lawrence Berkeley National Laboratory (LBNL) simulated earthquake scenarios on the Hayward fault and analyzed how the rupture and underground structure affect ground motion intensity along the fault.

“Using high-performance computing earthquake simulations, we are interested in learning what the ground motion for a typical magnitude 7 earthquake in the Bay Area could be, so that we can work with engineers to make sure that the infrastructure and buildings in the Bay Area can withstand this motion,” said author and LLNL scientist Arben Pitarka. “With that information, we can also start preparations for retrofitting some of the vulnerable structures.”

According to geological evidence, magnitude 7 earthquakes happen relatively often on the Hayward fault. The U.S. Geological Survey estimates a 14.3% chance of a 6.7 magnitude or larger event by 2034 and a 33% chance before 2043 — making the Hayward fault the most dangerous in the Bay Area.

To prepare for the worst, scientists must understand the seismic hazard in the region. Under a Department of Energy (DOE) project led by LBNL, the team created a simulation platform that includes two major modeling components: one that simulates the generation of seismic waves during the earthquake rupture and another that propagates the seismic waves through the earth.

“Since we don’t know exactly how the rupture will evolve during an expected earthquake — including the overall fault slip, hypocenter location and rupture speed — we rely on a large number of simulations in which we vary several modeling parameters, including those of the earthquake rupture model,” said Pitarka. “These large-scale simulations allow us to reduce the uncertainty in ground motion estimates associated with earthquake rupture.”

The LBNL and LLNL researchers used DOE’s exascale computing infrastructure to simulate 50 magnitude 7 earthquakes on the Hayward fault.

“With this new database, not only can we provide better estimates of the expected ground motion from this type of earthquake, but we can also locate areas that are susceptible to very strong shaking in the San Francisco Bay Area,” said Pitarka.

Locations near the Hayward fault are at high risk, especially those that fall inside a cone-shaped zone along the fault that starts at the epicenter and spreads on both sides of the fault. Due to the pulse-like nature of the ground motion created by the so-called “rupture directivity effect,” that area would experience strong shaking that is far more intense than normal and especially dangerous for tall or flexible buildings. Empirical ground motion prediction models are not well-constrained to account for this effect.

The simulations also revealed other areas that are susceptible to increased ground motion intensity: sedimentary basins and microbasins. For these bowl-shaped depressions in the earth’s shallow crust, such as the Livermore basin, the ground motion is amplified regardless of the earthquake location.

Going forward, the team aims to extend their simulations to model earthquakes on the San Andreas fault, which can produce magnitude 7.5 earthquakes or larger. The bigger the earthquake, the further the ground motion spreads and the more computational power is required to model it. They are also pushing the models to capture seismic waves with higher frequencies, which requires very detailed knowledge of the earth’s subsurface.

Closer to home, LLNL seismologists hope to improve the understanding of seismic hazard at the Livermore site, where a large earthquake on the Hayward fault or a moderate size earthquake on the nearby Greenville fault could cause significant damage to equipment that is sensitive to strong ground shaking.

This article originally appeared in Newswise. It was written by people at the

Topics Catastrophe Natural Disasters