Seismic data from 2016 reveals a rare bi-directional boomerang earthquake.
- An earthquake ran quickly east before turning west beneath the Atlantic Ocean near the equator in 2016.
- Such earthquakes are likely to pack significantly more destructive power.
- Land-based boomerang earthquakes may have been witnessed, but have never been recorded seismographically.
It was definitely an odd story Rosario García González told in the summer of 2010.
González is an elder of the indigenous Cucapah community in Baja, California/Mexico. He and his wife were in their trailer in Paso Inferior, about 12 miles south-southwest of Mexicali when they heard and felt the distinct, powerful rumble of earthquake moving across their valley. Looking outside, they watched as a cloud of light-colored dust was thrown up into the air along a path going in the opposite direction, as if a truck was retracing the earthquake's path. Except there was no truck.
It's not that scientists didn't believe González's story — they just couldn't figure out what he saw. Could an earthquake possible boomerang? The answer appears to be yes. A new study of seismic data has found clear evidence of another boomerang earthquake — technically a "back-propagating supershear rupture" — that shot back and forth deep beneath the Atlantic Ocean in 2016.
Boom and back
Reconstruction of Romanche fracture zone
The research was conducted by scientists from the University of Southampton and Imperial College, London in the U.K. First author Stephen Hicks of Imperial College says, "Whilst scientists have found that such a reversing rupture mechanism is possible from theoretical models, our new study provides some of the clearest evidence for this enigmatic mechanism occurring in a real fault."
The 2016 magnitude 7.1 quake occurred along the Romanche fracture zone — this is a 559 mile-long fault line near the Atlantic equator, about 650 miles west of the coast of Liberia.
Speaking to National Geographic, Hicks recalled the discovery of what at first seemed like a pair of pulses, which closer examination indicated might actually be two phases of the same quake. If so, the quake zipped eastward, and then west. "This was a weird sort of configuration to see," he says. Confirmation of the boomerang was provided by Ryo Okuwaki of Japan's University of Tsukuba via the identification of seismic echoes from the distant event.
"Even though the fault structure seems simple, the way the earthquake grew was not, and this was completely opposite to how we expected the earthquake to look before we started to analyse the data," admits Hicks.
When modeled, the data collected by 39 seismometers arrayed along the bottom of the ocean-floor gash depicted a temblor that moved rapidly in one direction before suddenly turning around and going back in the other at a blistering 11,000 miles per hour. This likely caused seismic waves to pile up similarly to what happens with air-pressure waves trigger a sonic boom, significantly magnifying the quake's power.
Rosario García González points to where the earthquake doubled back.
Image source: CISESE/USGS
While it's logistically simpler to record and study earthquakes on land thanks to the availability of seismometer networks, land-based temblors tend to track complex fault systems, with geological slips occurring in a series like falling dominoes. Sea-bottom quakes appear to be simpler, making it easier to discern their underlying mechanisms and travels.
Only a few boomerang quakes have ever been recorded, and examples of them on land are virtually nonexistent, making accounts such as González's that much more valuable. Clearly, quakes that double back on themselves stand to do considerably more damage than one-way shakers, allowing more outward propagation of destructive seismic waves in the direction of travel, an amount that would be doubled in a boomerang. Seismologist Kasey Aderhold tells National Geographic that "studies like this help us understand how past earthquakes ruptured, how future earthquakes may rupture, and how that relates to the potential impact for faults near populated areas."
Scientists developing computer models aimed at predicting seismic events haven't thus far been able to create worthy simulations of boomerang quakes, so the details provided the U.K. researchers provide some of the best information yet collected on these geologic oddities.
Minnesota earned its 'blue mark' in the 1975 Morris earthquake, which had its epicenter in the western part of the state.
- Californians, want to run away from the Big One? Head for Minnesota.
- As this map shows, the Gopher State is the least likely to be hit by earthquakes.
- Choose your new home wisely, though: even Minnesota has one earthquake-sensitive spot.
Not if, but when<img type="lazy-image" data-runner-src="https://assets.rebelmouse.io/eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpbWFnZSI6Imh0dHBzOi8vYXNzZXRzLnJibC5tcy8yMjc3NTAwOC9vcmlnaW4uanBnIiwiZXhwaXJlc19hdCI6MTY1Mjk4ODI3MX0.5T33e183P6FCkKaF2OeYN87pJSgKMnbuFmjS68p3TJQ/img.jpg?width=980" id="9893f" class="rm-shortcode" data-rm-shortcode-id="2dee8c6a6ec7c73c705d45b067c3113e" data-rm-shortcode-name="rebelmouse-image" alt="The Long Beach earthquake hit on 10 March 1933 with an estimated magnitude of 6.25 on the Richter scale." />
The Long Beach earthquake hit on 10 March 1933 with an estimated magnitude of 6.25 on the Richter scale.
Image: Nathan Callahan, CC BY 2.0<p>It's not if, but when: Californians live with the certainty that someday, <a href="https://the-big-one.scpr.org/stories/" target="_blank">the Big One will hit</a>. </p><p>The Big One is an earthquake with a magnitude of at least 7.8 on the Richter scale. Because of the plate tectonics at work under California, big quakes like that hit the area every 45 to 230 years. </p><p>The last one was more than 160 years ago. That's why paleoseismologist Kerry Sieh says the next one is likely to happen "within the lifetime of children in primary school today."</p><p>Here's how the United States Geological Survey (USGS) rates the hazard of a major earthquake in California in the next 30 years: </p><ul><li>60% chance of a 6.7-magnitude quake.</li><li>46% chance of a 7.0-magnitude quake.</li><li>31% chance of a 7.5-magnitude quake.</li></ul>It should be noted that the Richter scale is logarithmic in nature, meaning that a one-point increase in magnitude (e.g. from 6.7 to 7.7) represents a tenfold increase in amplitude. So, the Big One will be considerably stronger than the highest-magnitude quake considered by the USGS. When it hits, the Big One is likely to kill hundreds, hurt thousands and displace many more. It will cause widespread damage to buildings and infrastructure and start hundreds of fires. How do you put as much distance as possible between yourself and that apocalyptic prospect? Start with this earthquake hazard map.
Hazard everywhere<img type="lazy-image" data-runner-src="https://assets.rebelmouse.io/eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpbWFnZSI6Imh0dHBzOi8vYXNzZXRzLnJibC5tcy8yMjc3NTAxNS9vcmlnaW4uanBnIiwiZXhwaXJlc19hdCI6MTYzOTEzMzk1Nn0.ObHDJkYWtqif-bPnp0kqLqc30qZRiuDewFxCUdhCG1o/img.jpg?width=980" id="c0031" class="rm-shortcode" data-rm-shortcode-id="d46c7b8f9cf4db06eba76166982b9271" data-rm-shortcode-name="rebelmouse-image" alt="The earthquake hazard map of the United States." />
The earthquake hazard map of the United States.
Image: USGS, public domain<p>The Pacific coast is purple: the highest hazard. The entire west is shaded in colors denoting declining hazard. Only relatively small parts of the country are covered by the zone of lowest hazard:</p><ul><li>central and southern Texas;</li><li>most of Florida, Michigan, Wisconsin, Iowa, and North Dakota;</li><li>sizable chunks of Kansas, Nebraska, Montana, and South Dakota;</li><li>and tiny bits of Alaska, Colorado, New Mexico, Louisiana, Arkansas, Alabama, and Georgia. </li></ul><p>One state seems hazard-free, but that's only until you notice the blue spot in Minnesota's western bulge. </p><p>So, what do these colors actually denote? Earthquake hazard maps show the potential shaking hazard from future earthquakes. <br></p><p>The USGS defines earthquake hazard as the probability of ground motion over 50 years. That probability is determined by a region's geology and earthquake history. </p><p>The location of fault lines alone is not enough to determine quake hazard: a large earthquake can produce tremors at a relatively large distance from the actual fault line. </p><p>The colors on this earthquake hazard map correspond to <a href="http://www.isatsb.com/Seismic-Design-Category.php" target="_blank">Seismic Design Categories</a> (SDCs), which reflect the likelihood of seismic activity leading to ground motion of various intensities. <br></p>
Seismic resistance<img type="lazy-image" data-runner-src="https://assets.rebelmouse.io/eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpbWFnZSI6Imh0dHBzOi8vYXNzZXRzLnJibC5tcy8yMjc3NTAxOS9vcmlnaW4uanBnIiwiZXhwaXJlc19hdCI6MTYyNTk4MjU5N30.52qb_X6Mu7xus-lfXgBWxAr8Ib8ogRfnjJ8H_lohMsM/img.jpg?width=980" id="5f182" class="rm-shortcode" data-rm-shortcode-id="45ec9a1e5c056a2f8e5949aba7b15355" data-rm-shortcode-name="rebelmouse-image" alt="Damage caused by the 6.0-magnitude Napa County earthquake of 24 August 2014" />
Damage caused by the 6.0-magnitude Napa County earthquake of 24 August 2014.
Image: Matthew Keys, CC BY-SA 4.0<p>These SDCs are used to determine the level of seismic resistance required in building design and building codes. </p><ul><li>SDC level A (grey): Very small probability of experiencing damaging earthquake effects. </li><li>SDC level B (blue): Moderate-intensity shaking possible. Such shaking will be felt by all. Many will be frightened. Some furniture will be moved and some plaster will fall. Overall damage will be slight. </li><li>SDC level C (green): Strong shaking possible. Damage will be negligible in well-designed and well-constructed buildings; considerable in poorly-built structures.</li><li>SDC levels D0 (yellow), D1 (orange) and D2 (red): Very strong shaking possible. Damage will be slight in specially designed structures; considerable in ordinary substantial buildings, with partial collapse; and great in poorly built structures.</li><li>SDC level E (purple): This is near major active faults capable of producing the most intense shaking. Even in specially designed structures, the damage will be considerable. The shaking is intense enough to completely destroy buildings.</li></ul>
The Morris quake<img type="lazy-image" data-runner-src="https://assets.rebelmouse.io/eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpbWFnZSI6Imh0dHBzOi8vYXNzZXRzLnJibC5tcy8yMjc3NTAzMS9vcmlnaW4ucG5nIiwiZXhwaXJlc19hdCI6MTYzODIyNTczN30.OYlo64hJTvr6DF6aIeDdRtVIRmLRLl6n33B-a6hsKoc/img.png?width=980" id="bf33a" class="rm-shortcode" data-rm-shortcode-id="77ca44f7b8150aa88574327c2f920029" data-rm-shortcode-name="rebelmouse-image" alt="Morris quake, Stevens county, Minnesota" />
Minnesota earned its blue spot in 1975.
Image: USGS, public domain<p>This earthquake hazard map is not a snapshot of the past, but an evolving prediction of the future. The map is adapted as geological knowledge increases. But it is also partly based on past events – or more precisely the likelihood of their recurrence. </p><p>Minnesota earned its blue spot from the 1975 Morris earthquake. With its epicenter in Stevens County, it struck at around 10 am on July 9th of that year and had a magnitude of 4.6. It was the first seismic event recorded in the state since the Staples quake of 1917, and it was felt as far afield as the eastern Dakotas and northern Iowa. <br></p><p>Near the epicenter, plaster cracked and pictures fell off walls. In the town of Morris, two homes suffered damage to their foundations. Not quite California-sized, but for lack of comparison, probably Big Enough for the locals. </p>
Scientists discover how to predict megaquakes earlier to improve warning systems.
- Earthquakes of 7+ magnitude share a particular pattern, find seismologists.
- The pored over data of over 3,000 earthquakes to spot a "slip pulse".
- The scientists advocate using real-time GPS sensor data in early warning systems.
Vehicles driving over a crack on Highway 178, near Trona. This follows a 6.4-magnitude earthquake in Ridgecrest, California on July 4, 2019.
Credit: Frederic J. Brown/Getty Images
Natural disasters claim many more victims than terrorism, so why is funding in Europe and North America so out of balance? This negligence makes Neil deGrasse Tyson "embarrassed for our species".