CSU Long Beach -- October 3, 2003
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
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.