CSU Long Beach -- October 3, 2003

National Science Foundation Awards CSULB Geological Sciences Professor Grant to Study Mexico Coastal Seismic Area

The west-central coast of Mexico is amidst that nation’s most seismically active area, where the Cocos tectonic plate is slipping from the Pacific Ocean beneath the North American plate. However, there hasn’t been a major earthquake since 1911 in what is known by geologists as the Guerrero gap, so Maria Teresa Ramirez Herrera, professor of geological sciences at California State University, Long Beach, wants to know what is happening in this region.

With a recent $83,589 grant from the National Science Foundation (NSF), she and an international team of scientists and students are studying this area to better understand the geological history of the Guerrero gap and what happens during subduction zone earthquakes.

This has implications for other subduction areas such as the Juan de Fuca zone off the Pacific Northwest, where earthquakes could cause major damage in Eureka, Seattle or Vancouver. It’s also the source of volcanoes such as Lassen Peak in Northern California and Mount St. Helens in Washington.

The west coast of Mexico “is very well known for large earthquakes that have occurred in historical times, such as the 1985 earthquake (magnitude 8.1) that devastated Mexico City,” said Ramirez. Most recently, other earthquakes in 1995 (magnitude 8) and 2003 (7.4) devastated several coastal communities.

“There is a high probability of having an earthquake of magnitude more than 8.2,” she continued. “The groups that have been working on the Guerrero gap are scientists who focus on the present seismicity, and earthquakes occurring during historical times, and also geodesists who are working with global positioning systems.

“They have records from the 18th century and on, but we don’t know what happened before. That’s very important to answer because knowing if there were earthquakes of large magnitudes that hit that area before and when those occurred, we can determine a longer record of seismic activity in the area and hopefully establish reference intervals of earthquakes,” she said. “With the data that we have now, we can tell that the expectation is that every 70 years there might be a large earthquake, but the record is very small. We hope to find out geologic evidence for earthquakes that occur not only a few decades ago, but we could determine earthquakes that occurred hundreds and thousands of years ago.”

Ramirez heads a team including Andrew Cundy of the University of Sussex, England, who specializes in the geochemical aspects of coastal environment, and Vladimir Kostoglodov, a Russian seismologist working at the National Autonomous University of Mexico.

The team also includes two CSULB students, Matthew Sedor, who is working on his master’s degree, and undergraduate O. Kelly Murphy. The grant also enables Ramirez to add one new student this fall and next spring, giving them hands-on research experience. NSF has recognized Cal State Long Beach as having the second largest number of undergraduate and graduate students who go on to earn doctoral degrees in science or engineering from among the nation’s master’s level universities.

The team collected sediment samples this summer for analysis in CSULB’s high performance liquid chromatography-inductively coupled plasma mass spectrometer lab. “We are determining the amount of different chemical elements and those elements help us determine the different environments,” Ramirez explained. “I’m interested in finding relative changes in sea level. That is important because when there is a large magnitude earthquake, there are two possibilities, that the coast might subside, or there might be uplift.

“In terms of preliminary results that we see, there is a possibility that the coast has been subsiding for a long time. I’m cautious about saying this, but apparently there are buried sediments that indicate changes from brackish to marine water and tsunami events, so that means that earthquakes and tectonic activity might be associated with this. We also have dated sediments carbon that contain charcoal with radiocarbon, because once we know this is a tsunami event or there is a relative sea level change, we want to know when that happened and the way to do that is by dating,” she continued.

“These kinds of geology-paleoseismology studies help us to understand what is happening in other subduction zones like in Northern California, Oregon and Washington with the Cascadian subduction zone. There are some similarities and by understanding these processes in the Mexico subduction zone, we can understand what’s happening in other subduction zones— and to understand phemonena that are occurring in other areas of the world,” said Ramirez.

“One of the phenomenon that occurs there, at the Cascadian subduction, and that occurs at the Guerrero gap is what seismologists call slow or silent earthquakes,” where ground slippage takes place gradually over weeks, months or perhaps even years, often in such a subtle way that people wouldn’t necessarily recognize the movement as a quake. “This is one of the questions that I have and propose in this work—are these events capable of releasing all the energy or should we expect a big earthquake to occur in the future? My focus is that not all the energy is released by these events and that we should expect a large earthquake to occur.”

The team will continue its field work during a four-week visit to the region in December and January.

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