August 20, 2008
Stephen Hernández, a UNAVCO RESESS (Research Experience in Solid Earth Science for Students) intern since 2005, is second author on a widely noted paper published in Nature Geoscience’s May 2008 issue. The paper, Global ubiquity of dynamic earthquake triggering (Velasco et al.), explores the theory of earthquake triggering, but as a global phenomenon. This study looked at how the surface waves from large earthquakes can trigger smaller earthquakes all over the world, and not just in the vicinity of the larger quake. The authors describe this phenomenon as ubiquitous and independent of the tectonic environment of the main earthquake or subsequently triggered smaller earthquakes.
Hernández joined UNAVCO’s RESESS program at its inception in 2005. For his first summer as an intern, he worked with Dr. Kristine Larson at the University of Colorado in Boulder on identifying and characterizing multipath sources at the Parkfield GPS array. In 2006, Hernández took off for a three-week field season in Tanzania with Dr. Eric Calais of Purdue University to acquire GPS data on the East African Rift, and worked with David Phillips of UNAVCO on how to process high precision GPS data. He remained involved with the East African Rift project for several years.
Hernández is currently a math and physics major entering his senior year at the University of Texas at El Paso. He has worked on various geophysical problems as a research assistant in the Department of Geological Sciences, including dynamic and static triggering of large earthquakes, which led to the recently published paper, and the physics of wave propagation. Hernández enjoys the quantitative aspect of using physics-based techniques to solve geologic problems, while it is the humanitarian aspect of many geophysical problems that has kept him in the field of geology. He finds the direct societal impacts to be a strong motivating factor behind his work. The RESESS program is proud to see a protégé carry a research project through to publication.
RESESS is an internship program, initiated by UNAVCO, the Incorporated Research Institutions for Seismology (IRIS), the National Center for Atmospheric Research (NCAR), and the United States Geological Survey (USGS, Golden, CO), and sponsored in part by the National Science Foundation (NSF). The program combines structured mentoring, ongoing research internships, and a supported learning community for undergraduate and graduate students form underrepresented groups in order to increase the diversity within the solid earth sciences. RESESS participants, called protégés, come to Boulder, CO for a series of ten-week summer internships. The internships include a research project in collaboration with a solid earth scientist who is trained as a mentor, an experience of living and working with other students from underrepresented populations in science, and multidimensional mentoring from writing and communication, community, and peer mentors. Students who enter the program after their sophomore or junior year of college can participate for up to four years, which can help with the transition into graduate school. Please see the RESESS Website for more details.
Figure 1 - RESESS Intern Stephen Hernandez
Figure 2 - Detection Map showing possible triggered events recorded at 262 of 372 stations for the 2004 Sumatra–Andaman islands earthquake as recorded on each seismogram sorted by distance for all unclipped broadband data available at the DMC. Detections (circles) are plotted versus epicentral distance from the earthquake. Each detection is a potential local event. Solid lines represent short-arc surface-wave arrivals, and dashed lines represent long-arc arrivals.
Figure 3 - Histogram for detections summed along the Love-wave group velocity curve (4.3 km s-1) using 300 s bins. The vertical grey line is the arrival of the Love wave, whereas the bold horizontal line represents the mean (µ) for the time period before the arrival of the Love wave. The other two horizontal lines, solid and dashed, show the 95% and 99% confidence bounds, respectively. Zero time on the histograms is the time of the Love-wave arrival. Note that there is a peak at time zero and a secondary peak near 7,000 s ( 2 h) after the arrival of a short-arc Love wave (G1), which represents a cluster of events that occurred near the Nevada–California border, north of the Long Valley Caldera. Other peaks can be seen that we were unable to associate with any particular cluster.
Last modified: 2020-01-28 22:54:18 America/Denver