A massive earthquake could rock Los Angeles. In 1994, a substantial earthquake measured 7.3 on the Richter scale, jolting Los Angeles and the surrounding area. The quake caused $40 billion in damage and killed 57 people in southern California. In the past year, Los Angeles has had 291 earthquakes, with the strongest magnitude registered at 4.8 on the Richter scale.
Earthquake seismologists say that if the southern San Andreas Fault ruptures in a particular direction that southern California could expect an earthquake on an unprecedented scale, something not seen in the Los Angeles region in over 300 years.
Up until recently, seismologists had no method of predicting the effects of an earthquake before it happens. The National Science Foundation has created a new computer modeling study with the aim to help engineers design sounder structures. The “supercomputer” simulates how such a quake might progress from the fault line through the city. Such a fissure, as the computer models indicate, could reverberate through the L.A. area, triggering stronger ground motion than previously foreseen. The model shows that shaking in the Los Angeles Basin could feasibly be three times greater on average than in the surrounding L.A. areas.
Earthquake seismologist, Dr. Marine Denolle together with fellow researchers installed a number of seismometers along the San Andreas Fault line to put their method to test. They analyzed how vibrations generated by ocean waves, transmits through the ground. She and her colleagues then applied the collected data to induce 100 computer-simulated magnitude-7 “virtual earthquakes.”
By “synthesizing” the data gathered from the waves, Denolle and her colleagues used the virtual approach to reconstruct what would actually happen should a massive earthquake rock Los Angeles and propagate up the San Andreas Fault. According to Thomas Jordan, director of the Southern California Earthquake Center, it is a process to “trick the earth” with the purpose of giving researchers its response to a large-scale earthquake.
The seismologists have substantiated that with these virtual quakes, the geological structure underneath L.A. does amplify a quake’s shock waves. Angelenos would experience trembling as if they were next to the fault, even at 100 miles away from the actual rupture.
Characteristically, earthquakes create seismic waves that disperse as they radiate away from the source. Major cities such as Paris, Mexico City, Tokyo and Los Angeles lie atop a complex geological structure known as a sedimentary basin that changes the way energy transfers through the ground.
These soft foundations can magnify the extent of damaging cities like Los Angeles experiences during an earthquake. And while most Americans correlate earthquakes only with California, Denolle’s technique could prove useful for other parts of the United States too. For instance, both Pennsylvania and Ohio experienced earthquakes last year with a 4.0 magnitude that rattled residents.
The virtual quakes could forecast the threats looming over these states and even cities across the world. It would be especially beneficial to areas that have had no recent history of larger quakes.
According to earthquake seismologist, Greg Beroza, the benefit of this research, allows seismologists to “anticipate how the ground will shake” before earthquakes happen as opposed to waiting for an actual earthquake in order to calculate more about their effects.
The importance of predicting shaking from earthquakes is one of the most crucial factors seismologists can do to know how to create structures that will resist the quake shaking. By examining how these ambient waves move underground, researchers could predict the effects of much stronger waves from powerful earthquakes. Additionally, this computer study approach could also replicate “ancient quakes” to cast light on an area’s history.
While an earthquake of unprecedented magnitude could rock Los Angeles, the prospect of virtual earthquake research could significantly modify how buildings are designed in the future to minimize the destruction that rattles Angelenos and people worldwide.
by Dawn Levesque