An Overview
Major: Geophysics
Academic Affiliation: University of Texas at El Paso
Biography
Miriam Garcia was a first-year protégé and had just finished some undergraduate research during her junior year at the University of Texas at El Paso. Miriam joined the research team of Roger Bilham in the Department of Geological Sciences at the University of Colorado. PhD student Walter Szeliga was her direct supervisor and taught Miriam the necessary software package to conduct some computer modeling of an area of Pakistan that has experienced several significant earthquakes in the 1900’s. The modeling attempted to decipher whether the 1931 Mach earthquake was caused primarily by compression of the Indian Plate into the Eurasian Plate or by a west-dipping thrust fault which created the Bolan Pass fold.
Abstracts
2006- Modeling of vertical deformation associated with the 1931 Mach earthquake, Pakistan
The Kirthar Range in western Pakistan is the result of east-west compression caused by the indentation of the Indian Plate into the Eurasian Plate. The 1931 Mw 7.3 Mach earthquake resulted in 65 cm of local uplift on a leveling line through the Bolan Pass in the northern Kirthar Range. Previous studies modeled the fault as an east-dipping blind thrust with a top depth of 4 km and a bottom depth of 35 km, yet geologic cross-sections illustrated a blind wedge thrust system verging to the east with a horizontal décollement at 8 km. Extensive simulations of slip on this inferred structure suggested that this subsurface geometry could not be responsible for slip in the Mach earthquake. A west-dipping thrust was also considered a viable fault, as it was geologically capable of producing the anticlinal fold seen at the Bolan Pass. Forward elastic-modeling methods applied to the west-dipping thrust showed that the earthquake could not have occurred on a simple fault of this form either. A new approach, merging the wedge and west-dipping geometries may ultimately explain what happened in the 1931 earthquake sequence. Understanding fault constraints in Bolan Pass will give insight into correlations between the Mach earthquake and other seismic events during the 1930s.
2007- Field methods in volcanology: USGS Hawaiian Volcano Observatory (HVO), Center for the Study of Active Volcanoes (CSAV)
The Hawaiian Volcano Observatory (HVO) of the United States Geological Survey is used as a laboratory and classroom for future volcanologists. The Center for the Study of Active Volcanoes (CSAV) of the University of Hawaii at Hilo also hosts a field methods course in volcanology. As a volunteer at HVO and a CSAV student, one experiences firsthand the many physical and chemical aspects of volcano monitoring. On 17 June 2007, a magmatic intrusion, originating in Kilauea Caldera, traveled down the East Rift Zone. To see the effects of this intrusion, crack stations, Very Low Frequency (VLF) receivers, and geodetic leveling techniques were used to monitor the intrusion area. Other essential methods were applied. Gas geochemistry samples were taken in three separate locations to observe magma depth.
Distinguishing earthquake signals was part of the in-classroom, seismology section of the course. To measure deformation, a series of four GPS stations were set up, and a Light Detection and Ranging (LIDAR) instrument was introduced. As part of physical volcanology, scientists and students hiked out to the summit of Pu’u O’o and onto the fissure eruptions that started on 21 July 2007. A case study for the eruption of Eldfell Volcano in Iceland culminated the field class using previously learned tools and techniques. The effectiveness of volcano monitoring in the Eldfell situation was described, as well as recommendations for how scientists could have and can improve their techniques to reduce the impact of hazards in the area. Note: M. Garcia did these two volcano related educational experiences as an ancillary program to her required university summer field camp for 2007.
2008- Mogi model application on Grímsvötn Volcano, Iceland: continuous GPS data (2004-2008)
Grímsvötn is a subglacial volcano in Iceland with the highest eruption frequency of any of Iceland’s 30 volcanic systems during the past 800 years. It is located below the Vatnajökull ice cap and above the Iceland mantle plume. This study focused on the analysis of Grímsvötn’s recent deformation that will allow a better understanding of its behavior. This insight might also be applicable to the assessment of the risk of volcanic hazards, such as glacial floods (jökulhlaups), that affect the local population. The 2004-2008 time series data from the continuous GPS station (GFUM) was divided into five events. A Mogi model for each event was used to find characteristics of an equivalent point source that results in the same 3-D displacements displayed by GFUM. The Mogi code consists of four parameters: source geometry, observation point, and the Poisson’s ratio and shear modulus of the surrounding crust. Three values are output by the code: displacements, strains, and stresses in the east, north, and up directions. All five recent volcanic events at Grímsvötn were fitted to a volume change at a specific depth using the displacement output. The November 2004 eruption (event 2) resulted in a volume decrease of 23.5E-3 km3 at a depth of 2.55 km. All events had similar model results with the exception of event 4, which had a deep source,15.2 km. There were several aspects of the modeling process that contributed to errors in the results: 1) a non-spherical magma source, 2) an inhomogeneous crust, 3) lack of continuous GPS data at GFUM.