Quantcast
Environmental News for a Healthier Planet and Life

Help Support EcoWatch

Earthquake Forecast for Puerto Rico: Dozens of Large Aftershocks Likely

Science
A crack caused by an earthquake is seen in La Guancha boardwalk in Ponce, Puerto Rico on Jan. 9, 2020. RICARDO ARDUENGO / AFP via Getty Images

By Richard Aster

Multiple strong and damaging earthquakes in southern Puerto Rico starting around Dec. 28, 2019 have killed at least one person, caused many serious injuries and collapsed numerous buildings, including a multistory school in the town of Guánica that luckily was empty at the time. These quakes are the most damaging to strike Puerto Rico since 1918, and the island has been under a state of emergency since Jan. 6, 2020.



This flurry of quakes includes onshore and offshore events near the town of Indios and along Puerto Rico's southwestern coast. So far it has included 11 foreshocks – smaller earthquakes that preceded the largest event, or mainshock – with magnitudes of 4 and greater. Major quakes occurred on Jan. 6 (magnitude 5.8) and Jan. 7 (magnitude 6.4 mainshock), followed by numerous large aftershocks.

Seismologists like me are constantly working to better understand earthquakes, including advancing ways to help vulnerable communities before, during and after damaging events. The physics of earthquakes are astoundingly complex, but our abilities to forecast future earthquakes during a strong sequence of events in real time is improving.

Forecasting earthquakes is not a strict prediction – it's more like a weather forecast, in which scientists estimate the likelihood of future earthquake activity based on quakes that have already occurred, using established statistical laws that govern earthquake behavior.

An Undersea Fault Zone

Puerto Rico spans a complex boundary between the Caribbean and North American tectonic plates, which are sliding past each other in this region at a relative speed of about 2 centimeters per year. Over geologic time, this motion has created the Muertos Trough, a 15,000-foot depression in the sea floor south of the island.

This plate boundary is riddled with interconnected fault structures. The present activity is occurring on and near at least three interrelated large faults.

Multiple faults crisscross the eastern Caribbean. Those outlined in red have a potential to generate a large earthquake. The arrow at top right shows the direction of the North American plate's motion relative to the Caribbean plate. Red stars denote intensity centers for past earthquakes. USGS

Faults are pre-existing weak zones between stronger rocks. In response to surprisingly small force (stress) changes, they rapidly slip to produce earthquakes. The "hair-trigger" nature of fault slip means that predicting the precise timing, location and size of individual quakes is extremely challenging, if not impossible.

During an earthquake sequence, changing stresses act on nearby fault systems as stress is gradually redistributed within the earth. This process generates thousands of protracted aftershocks.

Many earthquake sequences simply start with the mainshock. But it is not especially rare for scientists to recognize after the fact that foreshocks were occurring before the main event. Improvements in earthquake instrumentation and analysis are helping scientists detect foreshocks more often, although we have not yet figured out how to recognize them in real time.

Will One Shock Lead to Another?

Researchers have known for over a century that the rate of earthquakes following a mainshock declines in a way that we can characterize statistically. There is also a well-established relationship between the magnitude of earthquakes and their relative number during an earthquake sequence. In most seismically active regions, for a decrease of one magnitude unit – say, from 4.0 to 3.0 – people can expect to experience about 10 times as 3s compared to 4s in a given time period.

Using such statistical relationships allows us to forecast the probability and sizes of future earthquakes while an earthquake sequence is underway. Put another way, if we are experiencing an aftershock sequence, we can project the future rate of earthquakes and what magnitudes we expect those quakes to have.

Richard Aster is a professor of geophysics and the department head at Colorado State University.
Disclosure statement: Richard Aster has received funding for earthquake research from the National Science Foundation, Los Alamos National Laboratory, Sandia National Laboratories and the U.S. Geological Survey. He is a past president of the Seismological Society of America (SSA) (2009-2011) and current chair of the board of directors of Incorporated Research Institutions for Seismology. Aster also chairs the U.S. Geological Survey's Advanced National Seismic System Advisory Committee, and is a member of the Southern California Earthquake Center Advisory Council.

Reposted with permission from The Conversation.

EcoWatch Daily Newsletter

Oregano oil is an extract that is not as strong as the essential oil, but appears to be useful both when consumed or applied to the skin. Peakpx / CC by 1.0

By Alexandra Rowles

Oregano is a fragrant herb that's best known as an ingredient in Italian food.

However, it can also be concentrated into an essential oil that's loaded with antioxidants and powerful compounds that have proven health benefits.

Read More Show Less
Brazilian President Jair Bolsonaro meets Ronaldo Caiado, governor of the state of Goiás on June 5, 2020. Palácio do Planalto / CC BY 2.0

Far-right Brazilian President Jair Bolsonaro, who has presided over the world's second worst coronavirus outbreak after the U.S., said Tuesday that he had tested positive for the virus.

Read More Show Less
Although natural gas produces fewer greenhouse gas emissions and other pollutants than coal or oil, it is a major contributor to climate change, an urgent global problem. Skitterphoto / PIxabay

By Emily Grubert

Natural gas is a versatile fossil fuel that accounts for about a third of U.S. energy use. Although it produces fewer greenhouse gas emissions and other pollutants than coal or oil, natural gas is a major contributor to climate change, an urgent global problem. Reducing emissions from the natural gas system is especially challenging because natural gas is used roughly equally for electricity, heating, and industrial applications.

Read More Show Less
The U.S. Environmental Protection Agency has approved two Lysol products as the first to effectively kill the novel coronavirus on surfaces, based on laboratory testing. Paul Hennessy / NurPhoto via Getty Images

The U.S. Environmental Protection Agency (EPA) recently issued a list of 431 products that are effective at killing viruses when they are on surfaces. Now, a good year for Lysol manufacturer Reckitt Benckiser just got better when the EPA said that two Lysol products are among the products that can kill the novel coronavirus that causes COVID-19.

Read More Show Less
U.S. Rep. Alexandria Ocasio-Cortez unveils the Green New Deal resolution in front of the U.S. Capitol on February 7, 2019 in Washington, DC. Alex Wong / Getty Images

By Judith Lewis Mernit

For all its posturing on climate change, the Democratic Party has long been weak on the actual policies we need to save us from extinction. President Barack Obama promised his presidency would mark "the moment when the rise of the oceans began to slow," and then embraced natural gas, a major driver of global temperature rise, as a "bridge fuel." Climate legislation passed in the House in 2009 would have allowed industries to buy credits to pollute, a practice known to concentrate toxic air in black and brown neighborhoods while doing little to cut emissions.

Read More Show Less
About 30,000 claims contending that Roundup caused non-Hodgkin's lymphoma are currently unsettled. Mike Mozart / CC BY 2.0

Bayer's $10 billion settlement to put an end to roughly 125,000 lawsuits against its popular weed killer Roundup, which contains glyphosate, hit a snag this week when a federal judge in San Francisco expressed skepticism over what rights future plaintiffs would have, as the San Francisco Chronicle reported.

Read More Show Less

Trending

Hundreds of sudden elephant deaths in Botswana aren't just a loss for the ecosystem and global conservation efforts. Mario Micklisch / Flickr / CC by 2.0

By Charli Shield

When an elephant dies in the wild, it's not uncommon to later find its bones scattered throughout the surrounding landscape.

Read More Show Less