Bryner reports that on July 4th, 2019, the most powerful 6.4 earthquake to hit Southern California in nearly 20 years struck a remote part of the Mojave Desert. A day later, an even stronger 7.1-magnitude earthquake struck on July 6, 2019, near Ridgecrest, California. Geologists know that though earthquakes beget earthquakes, but they also conclude that there's just a 5% chance that one quake will be followed by an even more powerful one. But that wasn't the only unusual feature of this earthquake duo in Southern California. Turns out, the earthquakes ripped Earth in weird ways. In particular, the temblors occurred on perpendicular faults in a zone known to be pretty complicated (more).
The magnitude-6.4 temblor struck the sparsely populated SoCal area at 10:33 a.m. local time on July 4, about 122 miles (196 kilometers) north-northeast of Los Angeles and just 11 miles (18 km) east-northeast of Ridgecrest. That quake was followed by several aftershocks, according to the U.S. Geological Survey (USGS). Geoscientists warned that a powerful aftershock of the same magnitude or greater was a possibility. Just a day later, at 8:19 p.m. local time, a quake of magnitude 7.1 — which is 11 times more powerful than the July Fourth event — struck about 6.8 miles (11 km) northwest of its predecessor. Today's monster quake caused injuries, fires and rockslides, and left more than 3,000 people without power. Shaking was felt as far away San Jose, about 260 miles (418 kilometers) from Ridgecrest, the Los Angeles Times reported.
Late Friday (July 5), a magnitude-7.1 quake struck near the town of Ridgecrest, California, just a day after the same region experienced a magnitude-6.4 quake. Experts say the fault system is growing and even more quakes are likely in the coming days. Another, even more powerful earthquake rocked Southern California on Friday (July 5). The temblor, which struck not far from the town of Ridgecrest in the Mojave Desert, registered as a magnitude 7.1, which is larger than the one that rocked the same general region on Thursday (July 4), according to the U.S. Geological Survey. That quake, a magnitude 6.4, was the largest to strike Southern California in 20 years, and was felt as far as Los Angeles.
Today's monster quake caused injuries, fires and rockslides, and left more than 3,000 people without power. Shaking was felt as far away San Jose, about 260 miles (418 kilometers) from Ridgecrest, the Los Angeles Times reported. Major damage is expected here in Ridgecrest, California after the earthquake. Our team is safe and we will be working to support evacuees.
Since the magnitude-6.4 quake on Thursday, more than 1,000 after shocks have struck the area, CBS News reported. So Friday's powerful ground-shaking was not a complete surprise. Southern California is a lot shakier than ever before realized. According to a new study, a tiny earthquake rumbles through the southern portion of the Golden State every 3 minutes. These temblors won't knock down walls or send palm trees swaying. In fact, they're too small for even typical seismic instruments to regularly detect. But their discovery reveals seismic activity that scientists couldn't previously detect. Understanding the full pattern of activity should help seismologists understand how larger earthquakes get started and how quakes can trigger one another. "The Earth's rocks in the deep subsurface are failing all the time," said study author Zachary Ross, a postdoctoral researcher in geophysics at the California Institute of Technology. "What really starts to come out is that these events, they're really communicating with each other in space and time." [13 Crazy Earthquake Facts]
Humanity is naturally most interested in large, damaging earthquakes, Ross told Live Science, the kind that take lives and bring cities to a standstill. But those quakes don't happen on the same time scale as human lifetimes. On a single fault, one big quake might occur every century, or even every thousand years. Smaller quakes are a lot more frequent. For each drop in unit of magnitude, there are 10 times more quakes, Ross said — so for every magnitude 7.0 temblor, for example, there are 10 magnitude 6.0 quakes, 100 magnitude 5.0 quakes and so on.
Even seismometers don't easily differentiate the smallest of these shakes from the background noise of the environment, Ross said. The standard catalog of Southern California quakes put out by Caltech and the U.S. Geological Survey catches everything of magnitude 1.7 and above, he said. Now, Ross and his team have found a way to tease out quakes as small as magnitude 0.3 from that same data. The trick, Ross said, is that two quakes with similar epicenters will show almost the same pattern of shaking on a seismogram, even if one is much larger than the other. The researchers used known earthquakes as templates, searching for smaller but otherwise identical squiggles in the earthquake record.
The method turned up a whopping 1.8 million tiny twins to known quakes over a period of 10 years. From 2008 to 2017, Southern California experienced an average of 495 tiny quakes a day, one every 174 seconds, Ross and his colleagues reported today (April 18) in the journal Science. As staggering as those numbers are, they're exactly what you'd expect given the rule of thumb of 10 times as many quakes per unit of magnitude, Ross said. "We get ten times as much information now, and it should be allowing us to test out all sorts of new things that we couldn't have done in the past," he said. One example: In 2012, California's Imperial Valley experienced a series of earthquakes known as the Brawley Earthquake Storm. There were hundreds of tiny quakes, and two slightly damaging ones reaching magnitudes of 5.3 and 5.5. Using the newly fleshed-out data set, Ross and his team found that this earthquake swarm actually began with 10 additional hours of subtle, previously unnoticed shaking. The team also used the data to investigate the aftermath of the 7.2-magnitude El Mayor-Cucapah earthquake that shook Baja California, Mexico, in 2010. There was a noticeable spike in extremely low-level quakes for the week after that shock at distances up to 170 miles (275 kilometers) away from the fault, the researchers found. These nearly undetectable shifts could explain how quakes affect each other over long distances, Ross said.
The same template-matching technique could be useful far beyond Southern California, Ross added. Any region or country with a good seismic network and high-quality data record could search their own history for tiny quakes, he said. "I think this is going to really lead to a whole new wave of scientific analysis," he said.
All in all, these earthquakes were centered in the desert. If such quakes occur in populated areas, the damage would be incredible (more). No sign of that but people need to be ready to go to safety should new quakes begin below populated areas. The U.S. Geological Survey offers earthquake alerts (more).
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