By Annie Reisewitz
The 1906 earthquake that devastated San Francisco marked a famous moment in history but it was a relatively anonymous quake some 50 years prior that showed just how much energy California’s faults can disperse.
In 1857, a magnitude-7.9 earthquake ruptured about 360 kilometers (225 miles) along California’s San Andreas Fault. It was the same magnitude as the San Francisco quake, but displaced the earth to a much greater extent. It moved the ground horizontally as much as nine meters (30 feet) at points along a stretch from Parkfield, Calif. to San Bernardino, Calif. The Fort Tejon earthquake, as it is now known, was one of the most powerful earthquakes ever recorded in U.S. history nonetheless caused only sparse damage around San Bernardino, which had 1,200 residents at the time.
Scientists say there is a 99 percent chance California will experience a magnitude-6.7 or greater earthquake in the next 30 years. With the average large earthquake occurring in Southern California every 150 years, a major quake is a reality that cannot be ignored.
As the state braces for the next major quake, scientists at Scripps Institution of Oceanography at UC San Diego are making major improvements to one of the field’s most fundamental tools—the seismometer—and developing early-warning systems they hope will save lives when the expected event finally happens. Transmissions from new instruments could outpace seismic waves, giving cities precious seconds to prepare.
Many earthquake sensors were developed at Scripps’ Piñon Flat Observatory, a research facility in the desert near Anza, California. The facility is located between two major faults, the San Andreas and San Jacinto, which makes it an ideal natural earthquake laboratory. Scientists from around the world come to Piñon Flat to test new instrumentation and monitor the more than 300 known active faults in the region in hopes of improving the understanding of the earthquake cycle and refining estimates of earthquake hazards.
FOREWARNED
Earth’s most famous fault, the San Andreas, is the meeting place for the North American and Pacific tectonic plates. The Pacific plate is slowly moving northwest, taking Los Angeles on a journey toward San Francisco. As these plates slip past each other tension builds and is eventually released in the form of earthquakes.
When the so-called “Big One” ruptures along the San Andreas Fault near Southern California’s Salton Sea, a scenario many scientists believe is among the most likely, it would take about one minute before Los Angeles starts shaking like a bowl of Jell-O. A minute of warning may be the city’s best chance for survival.
Scripps researcher Yehuda Bock, director of Scripps’ California Spatial Reference Center, installed the first real-time Global Positioning System (GPS) stations at Scripps’ Piñon Flat facility in 2004. Today, the system consists of more than 80 GPS stations throughout Southern California, offering a promising early-warning system for earthquakes, similar to one currently operating in Japan.
As the earth relieves some of its built-up tension, the California Real-Time Network (CTRN) monitors the ground motion from satellites roaming above and sends data streaming back every second to the Scripps campus in La Jolla, Calif., over UCSD’s High Performance Wireless Research and Education Network (HPWREN). When the system detects the first tremble of what will be a magnitude-6 or larger earthquake, it automatically triggers an email alert to subscribers.
“The critical step is to find someone to accept this information and react,” says Bock.
CRTN is working with the Southern California Earthquake Center (SCEC), the U.S. Geological Survey and UC Berkeley this year to link emergency services and public works throughout California to this early-warning system.
Bock’s system could help trigger shutdowns of critical facilities such as gas lines and signal train and mass transit operators to put on the brakes, as Japan’s does, potentially minimizing damage and loss of lives. To be more effective, the electronic alert system needs to automatically activate these emergency responses, something experts anticipate can happen in California within the next decade.
He anticipates expanding the network's operation throughout California by adding new GPS stations, incorporating data from seismic networks, and offering additional information available through a public-friendly web interface.
In addition to serving as an early-warning system for earthquakes, the network can also be used to forecast storms that are likely to cause flooding. Bock and colleagues have exported the technology to Indonesia as an early warning system for tsunamis and to Sicily to warn of volcanic eruptions, landslides, and tsunamis.
“The network is working 24/7 and is available to surveyors and others who require high precision GPS positioning,” Bock said. “It’s not just sitting around waiting for an earthquake to happen.”
QUIETER CONNECTIONS
Ink splattered on the wall next to an outdated seismograph at Piñon Flat reminds visitors of the region’s shaky history. Scientists have since replaced the ink- and paper- drum-based seismograph with electrical seismometers.
Scripps researchers are now giving current seismometers a needed facelift using the most modern technology.
The prototype earthquake sensor, which Scripps graduate student Jose Otero is testing in an underground seismic vault at Piñon Flat, could rival the STS-1, the most widely used broadband instrument currently in use, which he calls the “Cadillac of seismometers.”
The new instrument, jointly designed and built by Otero and Scripps researchers Mark Zumberge and Jon Berger employs fiber optics technology and interferometery, a method that can measure the distance of ground movement using beams of light. The technology offers scientists a quieter instrument that can better operate in some of the more extreme environments where seismologists are interested in listening to Earth’s rumblings.
The major upgrade over existing seismometers is in the removal of a direct electrical connection. The new sensor doesn’t require any electrical wires or circuit boards to operate, eliminating the constant and unavoidable hum, which accompanies an electrical connection. The earthquake sensor is better able to handle the stiflingly hot conditions where they typically operate, such as in holes 600 meters (1,969 feet) below ground, where temperatures can often exceed 150°C (302°F).
“Electronics often fail when they get too hot or remotely close to a lightning strike,” said Otero.
iSeis, as Otero’s interferometric seismometer is named, can operate far from its power source in the unforgiving remote environments in which scientists must deploy seismometers to locate earthquake epicenters. The instrument could also offer more precise measurement of the time it takes for seismic waves to travel and to determine their magnitude and direction.
The earthquake signals that Scripps scientists and other researchers are looking for are very small and weak. By lowering the output noise on the equipment, as iSeis does, researchers can better detect the smaller and more distant signals, potentially capturing something they would have otherwise missed.
“If the instrument noise is high, these signals can get lost,” says Otero.
iSeis connects to the nearby HPWREN network that runs through remote desert areas of Southern California, sending seismic data streaming back to the Scripps campus. It offers researchers faster data transmissions than the current system, which operates using satellites and telephone lines. Otero foresees his prototype being a viable competitor to traditional seismometers.
LOOMING THREAT
Driven by long internal processes that take hundreds of years, earthquakes have remained largely unpredictable to the cadre of scientists monitoring their every move.
Scientists are much closer to pinpointing the exact time and location of the next tremor than they were even a few decades ago. They can say with confidence that Californians will be jolted by a sizeable temblor at some point in the next 30 years, with the southern portion of the state being particularly vulnerable.
Scripps scientists continue to develop new earthquake monitoring systems to better understand earthquake triggers and to quickly detect the direction in which the destructive wave will travel, in hopes it can be outpaced before it arrives.
Researchers are also participating in efforts to prepare the public, government officials, and first responders for the Big One through events such as the November 2008 Great Southern California Shakeout. Emergency preparedness officials simulated a 7.8-magnitude earthquake during the Shakeout, one that ruptured 315 kilometers (196 miles) northwest along the San Andreas Fault from its southernmost point near the Salton Sea to Lake Hughes in Los Angeles County.
Scripps scientists believe the Salton Sea and surrounding region is the most seismically active region of the world and should experience a large earthquake sooner rather than later if the region follows historical patterns. Recent work by Scripps geophysicists Graham Kent, Neal Driscoll, Jeff Babcock, and others suggests that earthquakes that large magnitude 7 earthquakes on the San Andreas Fault have occurred roughly every 200 years in the region, yet it has been largely silent for the last 335 years.
By understanding how the earth works around fault zones, scientists can get even closer to pinpointing the causes, strength, and locations of earthquakes, information vital to saving lives and property.
Until the day arrives when scientists can forecast this most mysterious and dangerous of Earth’s natural hazards, Southern Californians need to be prepared for it to happen any day.
“Earthquakes happen and will continue to happen, so plan ahead and be ready,” said Otero.