Category: Earthquakes

7,1 Magnitude Earthquake Hits Near Ridgecrest In Southern California

A 7.1-magnitude earthquake rocked Southern California on Friday night — the second temblor to hit near Ridgecrest in less than two days.

The latest earthquake occurred 11 miles northeast of Ridgecrest, according to the US Geological Survey. It rocked buildings and cracked foundations, sending jittery residents out on the streets.

It comes a day after a 6.4-magnitude earthquake centered near Ridgecrest rattled the state Thursday. That earthquake has produced more than 1,400 aftershocks, scientists said.

Multiple fires and injuries have been reported in Ridgecrest — about 150 miles from Los Angeles — after Friday’s earthquake, Kern County spokeswoman Megan Person said. The county has activated an emergency operations center, the fire department tweeted.

The San Bernardino County Fire Department said it has received multiple reports of damage from northwest communities in the county.

“Homes shifted, foundation cracks, retaining walls down,” the department said. “One injury (minor) with firefighters treating patient.”

Localized power outages in LA

In central Los Angeles, Friday’s earthquake felt stronger than the one a day earlier, making buildings rock back and forth forcefully. Donald Castle, who lives in Porterville west of Ridgecrest, said his house shook for between 20 and 25 seconds.

“It was more of a shake than what we had on the Fourth. It lasted longer and was more rolling,” he said.

Public safety units are being deployed throughout the city ” to ensure safety and inspect infrastructure,” Los Angeles Mayor Eric Garcetti said.

The Los Angeles Fire Department said there were reports of wires down and localized power outages in some parts of the city. Fire crews are still surveying the city, it said, but no major damage to infrastructure has been identified so far.

The fire department is no longer in Earthquake mode and has determined there are no injuries or significant damage in Los Angeles city, chief Ralph M. Terrazas tweeted.

The shaking was felt in Mexico and Las Vegas

The shaking was felt as far as Mexico, according to the USGS website.

The NBA Summer League game between the New Orleans Pelicans and the New York Knicks in Las Vegas was postponed Friday following reports of the quake. Scoreboards and speakers near the ceiling of the arena shook when the earthquake hit.

Quakes are part of an ongoing system

CalTech seismologist Lucy Jones said Friday both earthquakes are part of an ongoing sequence, of a “very energetic system.”

The latest 7.1 earthquake was the mainshock, while Thursday’s 6.4 magnitude shake was a foreshock, according to Jones. She said Friday’s earthquake was 10 times stronger than the one a day prior.

The 7.1 magnitude shake was five times bigger than Thursday’s, but released 11 times the amount of energy than the 6.4 shake, CNN Meteorologist Brandon Miller said.
Officials are not ruling out that there could be more earthquakes coming.

California Gov. Gavin Newsom said he has activated the state emergency operation center to its highest level.

“The state is coordinating mutual aid to local first responders,” he tweeted Friday night.

Magnitude 6.4 Earthquake Rattles Southern California

A magnitude 6.4 earthquake rattled a large swath of Southern California on Thursday morning, according to USGS.

There are no immediate reports of damages or injuries.

The quake hit at 10:33 a.m. near the town of Ridgecrest.

It was originally recorded as a 6.6 magnitude earthquake.

The quake was felt in Bakersfield minutes after it struck. People from the desert to the Pacific coast in Southern California reported feeling it.

Study Reveals Key Factor In Himalayan Earthquake Rupture

The Himalayan orogenic belt produces frequent large earthquakes that impact population centers for a distance of over 2500 km. In the central region, the 2015 Gorkha earthquake in Nepal, with moment magnitude (MW) 7.8, partially ruptured a ~120-km by 80-km patch of the Main Himalayan Thrust (MHT), the detachment that separates the underthrusting Indian plate from the overriding Himalayan orogeny.

The rupture highlights important scientific questions about Himalayan formation and seismic hazards. These questions include how to distinguish between different possible geometries of the MHT, and how to better define the structural causes and locations of rupture segmentation both across-strike and along-strike in the orogenic belt.

A study led by Prof. BAI Ling from the Institute of Tibetan Plateau Research (ITP) of the Chinese Academy of Sciences revealed that the rupture length of the 2015 MW 7.8 Gorkha earthquake was likely controlled by spatial (both along- and across-strike) variations in the Main Himalayan Thrust.

The researchers combined seismic waveforms from several different deployments, including 22 seismic stations ITP had deployed along the China-Nepal border with an average elevation of 4.5 km prior to the earthquake. Using arrival times and waveform modeling, they determined source parameters of earthquakes, velocity structures and discontinuity topography in and around the source area.

The study showed that the MHT exhibited clear lateral variation along the geologic strike, with the Lesser Himalayan ramp having moderate dip on the MHT beneath the mainshock area, and a flatter and deeper MHT beneath the eastern end of the aftershock zone.

Following these observations, the impetus now is to image the entire 2,500-km Himalayan front to determine the morphology of the MHT and the likely controls on the maximum magnitude of rupture that can be accommodated in different parts of this convergence zone.

The study, entitled “Lateral variation of the Main Himalayan Thrust controls the rupture length of the 2015 Gorkha earthquake in Nepal,” was published in Science Advances.

Tsunamis Warning Lifted In Japanese Coastal Regions After Earthquake

Japan’s meteorological agency has lifted an earlier tsunami warning, after a 6.8 magnitude earthquake was recorded at 10:22 p.m. Tuesday (9:22 a.m. ET) off the coast of Yamagata Prefecture in the north of the country.

The agency had originally warned that tsunamis were “expected to arrive imminently” in the coastal areas of Yamagata, Niigata and Ishikawa, with an advisory issued for four coastal regions.

The meteorological agency has advised residents to evacuate those coastal regions immediately and to not enter the sea or approach the coastal regions until the advisory has been lifted.

Slight sea-level changes may be observed in coastal regions, but no tsunami damage is expected, it added.

In March 2011, Japan was hit by a 9.0 magnitude earthquake, its worst ever. The massive quake rocked the country and triggered an enormous tsunami that resulted in the country’s worst nuclear disaster.

The earthquake was so strong that it permanently moved Japan’s main island, Honshu, more than two meters to the east. Its impact also raised huge waves up to 40 meters (approximately 131 feet) high that, as people were still reeling from the aftershocks, began crashing into the coast.

In Fukushima, approximately 256 kilometers (159 miles) north of Toyko, three reactors at the Fukushima Daiichi nuclear plant melted down, releasing radioactive materials into the air.

Nearly 20,000 people died in the earthquake and subsequent tsunami and nuclear meltdown, with more than 100,000 people evacuated from the area.

Big Earthquakes Might Make Sea Level Rise Worse

A GEOLOGIC ONE-TWO punch rocked the South Pacific in September 2009, as a magnitude 8.1 earthquake struck off the coast of the island nation of Samoa, followed mere moments later by a similarly intense temblor. A towering tsunami soon crashed onto the shores of islands nearby, leaving more than 180 dead and communities in ruins in Samoa, the neighboring U.S. territory of American Samoa, and surrounding islands.

But a new study, published in the Journal of Geophysical Research: Solid Earth, reveals that the quakes also sparked a slow-burning danger for the more than 55,000 residents of American Samoa: sea level rise that is five times as fast as the global average.

Like other island and coastal regions around the world, Samoa and American Samoa are facing encroaching waters as our warming world sends sea levels soaring at accelerating rates. In the wake of the mega-quakes, though, the researchers discovered that these Pacific islands are also sinking. The situation is particularly concerning for American Samoa, where the team estimates that, over the next 50 to a hundred years, local sea levels could rise by roughly a foot in addition to the anticipated effects of climate change.

While the contributions of big earthquakes won’t be the same everywhere, the discovery emphasizes the sometimes overlooked effects that geology can have on the increasing number of people around the world who call coastlines home. (Also find out how powerful quakes are priming the region around Mount Everest for a huge disaster.)

“Everybody is talking about climate change issues … but they overlooked the impact of the earthquake and associated land subsidence,” says study leader Shin-Chan Han of the University of Newcastle, Australia, referring to documents from regional governments on sea level rise.

“This is a really important thing to point out,” says geophysicist Laura Wallace of the geoscience consultancy firm GNS Science, Te Pū Ao, in New Zealand, who was not involved in the study. “It obviously has a big impact on the relative sea level changes people are going to see in places like [the Samoan islands].”

Geologic geometry

Plate tectonics is constantly reshaping the surface of our planet—a role particularly evident during an earthquake. Generally speaking, these events occur where tectonic plates are colliding or sliding against each other, building up geologic stress. When that pent-up energy is released suddenly, it can send blocks of the planet’s crust careening out of place. (Find out how smaller “hidden” earthquakes are affecting California.)

But not all the change from a big earthquake is immediate. Unlike the rigid crust, the rocks of the mantle below flow like cold molasses and gradually adjust to the sudden surface jolt, Wallace says. This can cause either sinking or uplift of the land that can continue for decades after a temblor strikes.

This prolonged landscape deformation is what intrigues Han. For years, he’s scoured data from the Gravity Recovery and Climate Experiment, or GRACE, satellites to hunt for the rise and fall of land after a quake. This satellite duo orbited Earth in a line from 2002 to 2017 and precisely tracked the gap between the spacecraft. As they passed over zones with slightly more mass, and thus stronger gravity, the leading craft would feel the tug just before the trailing one. This tweaked the space in between and registered as a wobble in the planet’s gravitational field that can reveal changes in the landmass below.

In the case of the 2009 earthquake, such changes were minute on a day-to-day basis. But eventually, the effects were large enough that Han saw something strange happening in the Samoan islands while poring over the GRACE data.

A rare coincidence

The 2009 event was a particularly unusual earthquake that initially baffled scientists, since the pair of powerful temblors ripped through the Earth nearly at the same time. One broke along a so-called normal fault, created due to the flex of the oceanic crust as it plunges under another tectonic plate in what’s known as a subduction zone. Another quake broke within the subduction zone due to the compressive forces of the colliding plates.

The researchers investigated the lingering impacts of these quakes using a combination of GRACE data and local GPS and tide gauge records. They then built a computer model to tease apart the complex interplay between the temblors and what is happening at the surface.

This data showed slow sinking of the landscape, driven primarily by the normal-fault quake. This particular earthquake causes one side of the landscape to fall in relation to the other, which sent the nearby islands sinking downward.

The team found that nearly a decade after the event, the island of Samoa has sunk by roughly 0.4 inches a year. The situation is particularly acute for American Samoa, which has seen more than 0.6 inches of subsidence each year, and it doesn’t look like it’s stopping anytime soon.

The pace outstrips the estimated rate of global sea level rise, which is creeping upward at some 0.13 inches a year. Flooding and seawater intrusion in freshwater aquifers are already grave concerns for residents of American Samoa, Han says, and the latest find only adds to the worry.

Bathtub oceans

This latest study emphasizes the need for greater awareness and continued monitoring to mitigate the potential effects of mega-quakes, Wallace says. However, predicting such sea level effects before an earthquake strikes is not feasible, since earthquake prediction itself remains elusive.

“This might be a problem that suddenly causes you heartburn next week,” Freymueller says, “or it might not cause any problem for the next century.”

This latest study emphasizes the need for greater awareness and continued monitoring to mitigate the potential effects of mega-quakes, Wallace says. However, predicting such sea level effects before an earthquake strikes is not feasible, since earthquake prediction itself remains elusive.

“This might be a problem that suddenly causes you heartburn next week,” Freymueller says, “or it might not cause any problem for the next century.”

Scientists Find Telling Early Moment That Indicates A Coming Megaquake

Scientists combing through databases of earthquakes since the early 1990s have discovered a possible defining moment 10-15 seconds into an event that could signal a magnitude 7 or larger megaquake.

Likewise, that moment—gleaned from GPS data on the peak rate of acceleration of ground displacement—can indicate a smaller event. GPS picks up an initial signal of movement along a fault similar to a seismometer detecting the smallest first moments of an earthquake.

Such GPS-based information potentially could enhance the value of earthquake early warning systems, such as the West Coast’s ShakeAlert, said Diego Melgar, a professor in the Department of Earth Sciences at the University of Oregon.

The physics-heavy analyses of two databases maintained by co-author Gavin P. Hayes of the U.S. Geological Survey’s National Earthquake Information Center in Colorado detected a point in time where a newly initiated earthquake transitions into a slip pulse where mechanical properties point to magnitude.

Melgar and Hayes also were able to identify similar trends in European and Chinese databases. Their study was detailed in the May 29 issue of the online journal Science Advances.

“To me, the surprise was that the pattern was so consistent, Melgar said. “These databases are made different ways, so it was really nice to see similar patterns across them.”

Overall, the databases contain data from more than 3,000 earthquakes. Consistent indicators of displacement acceleration that surface between 10-20 seconds into events were seen for 12 major earthquakes occurring in 2003-2016.

GPS monitors exist along many land-based faults, including at ground locations near the 620-mile-long Cascadia subduction zone off the U.S. Pacific Northwest coast, but their use is not yet common in real time hazard monitoring. GPS data shows initial movement in centimeters, Melgar said.

“We can do a lot with GPS stations on land along the coasts of Oregon and Washington, but it comes with a delay,” Melgar said. “As an earthquake starts to move, it would take some time for information about the motion of the fault to reach coastal stations. That delay would impact when a warning could be issued. People on the coast would get no warning because they are in a blind zone.”

This delay, he added, would only be ameliorated by sensors on the seafloor to record this early acceleration behavior.

Having these capabilities on the seafloor and monitoring data in real time, he said, could strengthen the accuracy of early warning systems. In 2016, Melgar, as a research scientist at Berkeley Seismological Laboratory in Berkeley, California, led a study published in Geophysical Research Letters that found real time GPS data could provide an additional 20 minutes of warning of a possible tsunami.

Japan already is laying fiber optic cable off its shores to boost its early warning capabilities, but such work is expensive and would be more so for installing the technology on the seafloor above the Cascadia fault zone, Meglar noted.

Melgar and Hayes came across the slip-pulse timing while scouring USGS databases for components that they could code into simulations to forecast what a magnitude 9 rupture of the Cascadia subduction zone would look like.

The subduction zone, which hasn’t had a massive lengthwise earthquake since 1700, is where the Juan de Fuca ocean plate dips under the North American continental plate. The fault stretches just offshore of northern Vancouver Island to Cape Mendocino in northern California.

6.6 Magnitude Earthquake Hits Off Coast Of El Salvador

A strong earthquake has hit off the coast of El Salvador, sending frightened residents running out of their homes in the predawn hours.

The U.S. Geological Survey says the quake had a preliminary magnitude of 6.6. Its epicenter was about 17 miles south-southeast of La Libertad, a suburb of the regional capital, Santa Tecla, and it was recorded at a depth of 65 kilometers (40 miles).

The earthquake was felt strongly in the capital, San Salvador, Thursday morning. People left their homes with flashlights, and power was knocked out in at least some areas.

At least seven aftershocks of between magnitude 4.1 and 5.0 were recorded, while El Salvador’s Ministry of Environment and Natural Resources warned of a possible tsunami and advised people to stay away from the Pacific Ocean for the next four hours.