Earthquake Hazards in the Chehalis Basin Region
State of Washington Capitol Budget Project, 2018-present
In 2005, the Chehalis River near Centralia, WA experienced catastrophic flooding. Among other effects, this flood closed a section of I-5. The state of Washington wishes to prevent this from happening in the future and is looking into ways of controlling river flow during powerful rain events. Any structure built in the region for this purpose should be properly engineered to handle the ground shaking during a major earthquake. Enter the Doty fault: a large, east-west trending reverse fault in this region of similar size to the active Seattle fault. It is very poorly understood and may be a hazard to the Chehalis/Centralia region. In this project, we seek to map the length of the fault, determine its total offset, and define its status as an active fault to understand the likelihood of it producing a major earthquake and in that event, what magnitude might be possible. Moreover, we are looking for subsidiary, associated faults that are not currently on the map. Our work is also contributing to StateMap quadrangle mapping efforts in the Adna, Rochester and Oakville regions.
Abstracts:
Anderson, M. L., Lau, T., von Dassow, W., Reedy, T., Staisch, L., Cakir, R., Sadowski, A., Polenz, M., Becerra, R., Toth, C., Steely, A., Walsh, T., Norman, D., Sherrod, B., 2018, The Doty fault network: 3-D regional deformation applied to seismic hazard characterization in the forearc of Washington State, Fall Meeting, AGU, Washington, D.C., December 10-14, Abstract T13I-0356.
Lau, T., Anderson, M. L., Polenz, M. Sadowski, A., Becerra, R., Toth, C., Cakir, R., von Dassow, W., Reedy, T., Staisch, L., Steely, A., Walsh, T., Norman, D., Sherrod, B., 2018, Integrated geophysical investigation and 3-D fault characterization of the Rochester and Adna 7.5’ quadrangles, Thurston and Lewis counties, Washington, Fall Meeting, AGU, Washington, D.C., December 10-14, Abstract T13I-0355.
Active Faults in the Greater Seattle Urban Area
Washington State, 2005-present
I started this project during my postdoc at the USGS in Menlo Park. My original goal was to evaluate existing structural models of the active Seattle fault zone created from active source seismic data. Why did this need to happen? Because there were three very different interpretations of the seismic data collected in the same region! My original plan proposed testing the models for structural viability (are they balanced?) and determining if they would predict potential field anomalies from previously collected datasets. I ran into two roadblocks: 1) I had almost no physical property measurements (density and magnetic properties) for rocks the region (and it turns out a woefully simplified understanding of the geology), and 2) The gravity database did not have enough measurements to support the modeling I proposed. Now 10 years later, I have developed (with the kind support of my fellow geologists at the Department of Natural Resources) a rock property database containing 450+ samples and covering 20+ formations and their subunits, and assembled > 2000 new gravity measurements covering the Seattle fault zone as well as others in the region. Along the way, I participated in producing 10 new 7.5 minute geologic quadrangles in the eastern Puget Lowland. This work has supported many student research projects, but now I am turning the mountains of data and analyses into papers bearing on the location of previously unknown faults in the region and the resulting earthquake hazards. I hope you will be seeing them very soon.
Select Maps:
Allen, M. D., Mavor, S. P., Tepper, J. H., Nesbitt, E. A., Mahan, S. A., Recep, C., Stoker, B. A., Anderson, M. L., 2017, Geologic map of the Maltby 7.5-minute quadrangle, Snohomish and King Counties, Washington: Washington Division of Geology and Earth Resources Map Series 2017-02.
Dragovich, J. D., Mavor, S.P., Anderson, M. L., Mahan, S. A., MacDonald, Jr., J. H., Tepper, J. H., Smith, D. T., Stoker, B. A., Koger, C. J., Cakir, Recep, DuFrane, S. A., Scott, S. P., Justman, B. J.*, 2016, Geologic map of the Granite Falls 7.5-minute quadrangle, Snohomish County, Washington: Washington Division of Geology and Earth Resources Map Series 2016-03, 1 sheet, scale 1:24,000, 63 p. text.
Dragovich, J. D., Anderson, M. L., Mahan, S. A., Koger, C. J., Saltonstall, J. H., MacDonald, J. H. Jr., Wessel, G. R., Stoker, B. A., Bethel, J. P., Labadie, J. E., Cakir, R., Bowman, J. D., DuFrane, S. A., 2011, Geologic map of the Monroe 7.5-minute quadrangle, King and Snohomish Counties, Washington: Washington Division of Geology and Earth Resources Open File Report 2011-1.
Dragovich, J.D., Walsh, T.J., Anderson, M.L., Hartog, R., DuFrane, S.A., Vervoot, J., Williams, S.A., Cakir, R., Stanton, K.D., Wolff, F.E., and Norman, D.K., 2008, Geologic map of the North Bend 7.5-minute quadrangle, King County, Washington, Washington Division of Geology and Earth Resources Geologic Map GM-73, 42 x 36 in. color sheet, scale 1:24,000, with 39 p. text, Washington State Department of Natural Resources.
Other maps & reports listed in my Scientific CV.
Publications:
Blakely, R. J., Sherrod, B. L., Hughes, J. F., Anderson, M. L., Wells, R. E., Weaver, C. S., 2009, The Saddle Mountain fault, Olympic Peninsula, Washington: Western boundary of the Seattle uplift: Geosphere, v. 5, no. 2, p. 105-125.
Select Abstracts:
INVITED Anderson, M. L., Dragovich, J. D., Mahan, S. A., MacDonald, J. H., Koger, C. J., Allen, M., Mavor, S., Blakely, R. J., Wells, R. E., 2017, No strain left behind: the Puget Lowland neotectonic fault network, Geological Society of America Annual Meeting, Seattle, WA, October 22-25, Abstract no. 210-1
INVITED Wells, R. E., Blakely, R. J., Anderson M., 2017, Siletzia, Yellowstone and the Farallon plate beneath North America, Geological Society of America Annual Meeting, Seattle, WA, October 22-25, Abstract no. 321-2.
INVITED Anderson, M. L., Waters, K., Dragovich, J., Blakely, R. J., Wells, R. E., 2015, New determination of the shape of the Seattle basin, Washington from gravity and magnetic data: Implications for seismic ground motion and crustal faults, Fall Meeting, AGU, San Francisco, CA, December 14-18, Abstract GP31B-06.
Anderson, M. L., Blakely, R. J., Wells, R. E., Dragovich, J., 2011, Eastern boundary of the Siletz terrane in the Puget Lowland from gravity and magnetic modeling with implications for seismic hazard analysis: Fall Meeting, AGU, San Francisco, CA, December 5-9, Abstract GP33B-06.
Anderson, M. L., Blakely, R. J., Brocher, T. M., Pratt, T. L., Wells, R. E., Haugerud, R., Bush, M., 2006, Structure of the Seattle uplift from seismic, gravity, magnetic, geologic, and geomorphic data: Eos Trans. AGU, 87 (52), Fall Meeting Suppl., Abstract T41A-1554.
Geothermal Play-Fairway Analysis of Washington State Prospects
DOE, USGS, Washington Department of Natural Resources Co-sponsored Interdisciplinary Research Investigation, 2016-2017
In 2016, I was invited to join an interdisciplinary team of scientists charged with evaluating three locations in the Cascades Mountains in Washington State for geothermal power development. Before I learned about the project, I had assumed there were already many geothermal power plants in the Cascades, an area of volcanic activity and high heat flow. Not so. I appreciated the opportunity to work towards increasing the U.S. renewable power capacity in a region I know well. The team collected new geophysical data (seismic, gravity, magnetic and magnetotelluric) and mapped the geology of three regions: the Wind River Valley, the Mt. St. Helens seismic zone (just north of the volcano) and an area east of Mt. Baker. My part in the project was coordinating and leading (in collaboration with Brent Ritzinger, USGS) a team of young scientists and students collecting the gravity and magnetic data. I created the potential fields maps, analysis and subsurface geologic models for the Mt. St. Helens seismic zone.
Reports:
Forson, C., Steely, A., Cladouhous, T., Swyer, M., Davatzes, N., Anderson, M., Ritzinger, B., Glen, J., Peacock, J., Schermerhorn, W., Burns, E., Stelling, P., 2017, Geothermal play-fairway analysis of Washington State prospects: Phase 2 Technical Report, Washington State Department of Natural Resources Report, 232 p.
Forson, C., Steely, A. N., Cladouhos, T., Swyer, M., Davatzes, N., Anderson, M., Ritzinger, B., Glen, J., Peacock, J., Schermerhorn, W., Burns, E., Stelling, P., 2017, Geothermal play-fairway analysis of Washington State prospects: Phase 2 report and phase 3 proposal, Department of Energy Internal Report.
Geophysical Imaging of the Water Table, U.S. Air Force Academy, Colorado Springs
CC and Mellon-Sponsored Summer Research for Students with Hydrology Interests, 2014-2015
This was a small project that nevertheless supported course work for two iterations of my Introductory Geophysics class at CC, and one student thesis. The students did all the hard work! All of the projects were geared towards investigating the depth of the water table under a building fitted with a ground source heat pump to determine feasibility of extending pipes into the groundwater. My thesis student (below) mapped the water table from the building to Monument Creek to evaluate if the groundwater system is losing or gaining in this region. He concluded that the water table is too deep under the building to effectively connect the ground source heat pump to it, but that likely saved the Academy some dollars in excavation fees!
Thesis:
Hess, M., 2017, Investigating the Water Table on the Air Force Academy Grounds Beneath Jack’s Valley, Colorado College Senior Thesis.
Geophysical prospecting in Pueblo Viejo, Costa Rica
CC-Natural Science Division-Sponsored Summer Research Reconnaissance Trips, 2012-13
My fellow CC professor Esteban Gomez in the Anthropology Department invited me and a student to join him in Costa Rica for two summers, evaluating two archeological sites on the Nicoya Peninsula. How could I say no? The first summer we collected ground magnetic data to find structures extending from and surrounding a test pit. The next summer we collected electrical resistivity data to pair with the ground magnetic data for interpretation. Our data helped Dr. Gomez’ Costa Rican colleagues apply for permits to excavate the site.
And there were so many butterflies!
Collaborative Research: Formation of basement-involved foreland arches: An integrated EarthScope experiment
NSF EarthScope Research Project #0843889, Bighorn Mountain region, Wyoming, 2009-present
Since my days as a graduate student, basement arches (a.k.a. “basement-cored uplifts”) have fascinated me. Under “normal” mountain building processes, faults utilize natural weaknesses in thick sedimentary sequences to stack sheets of rock rather like building blocks or dominoes, to create extensive mounds of rock forming an orogenic mountain belt. Basement arches, in contrast, are seemingly isolated ranges separated by basins, and the faults that bound them penetrate deep into the basement rock. The mechanics of the creation of such mountains are still debated in the tectonic community and this project was devised to understand these mechanics. Do the faults penetrate to the Moho? Do they meet a decollement in the mid-crust? Or are they simply a surface manifestation of more ductile (bending) processes deeper in the crust? I was a co-principal investigator for deploying thousands of seismometers across the Bighorn Mountain range (BASE) with the goal of imaging the crust and Moho to answer these questions. I was predominantly responsible for deploying the broadband component of the seismic network and with the help of my students, analyzing the data for mantle deformation via shear-wave splitting analysis. Surprisingly, we have found strong evidence that inherited Archean structures in the crust and/or mantle influenced where and how the mountains formed!
Publications:
O’Rourke, C., Sheehan, A. F., Erslev, E. A., Anderson, M., 2016, Small-magnitude earthquakes in north-central Wyoming recorded during the Bighorn Arch Seismic Experiment, Bulletin of the Seismological Society of America, v. 106, p. 2320-2331, doi:10.1785/0120160035.
Worthington, L. L., Miller, K. C., Erslev, E. A., Anderson, M. L., Chamberlain, K. R., Sheehan, A. F., Yeck, W. L., Harder, S. H., Siddoway, C. S., 2015, Crustal structure of the Bighorn Mountains region: Precambrian influence on Laramide shortening and uplift in north-central Wyoming, Tectonics, v. 35, no. 1, p. 208-236.
Yeck, W. L., Sheehan, A. F., Anderson, M. L., Erslev, E. A., Miller, K. C., Siddoway, C. S., and the BASE Seismic Group, 2104, Structure of the Bighorn Mountain region from teleseismic receiver function analysis: implications for the mechanics of Laramide shortening, Journal of Geophysical Research: Solid Earth, v. 119, no. B9, 7028-7042.
Anderson, M., Miller, K., Beck, S., Jadamec, M., 2014, Workshop Report: Modern and ancient basement arches and the connection to flat slab subduction: inSights, the EarthScope Newsletter, Fall issue, p. 3.
Select Abstracts:
Erslev, E. A., Sheehan, A. F., Miller, K. C., Anderson, M., Siddoway, C. S., Yeck, W., Worthington, L. L., Aydinian, K., O’Rourke, C., 2013, Laramide mid-crustal detachment in the Rockies: Results from the NSF/EarthScope Bighorn project, Geological Society of America Annual Meeting, Denver, CO, October 27-30, Paper no. 15-7.
Sheehan, A., Anderson, M. L., Alvarado, P. M., Beck, S. L., Erslev, E., Gilbert, H. J., Miller, K. C., Ridgway, K. D., Worthington, L. L., Yeck, W. L., Zandt, G., 2013, Deep crustal imaging of thick-skinned foreland fold and thrust belts: The Rocky Mountains and the Sierras Pampeanas, AGU Meeting of the Americas, Cancun, Mexico, May 14-17, Abstract T41A-07.
Thayer, D., Anderson, M. L., Hornbuckle, J., Ufret, T. N., Erslev, E., Sheehan, A. F., 2011, Constraining lithospheric and asthenospheric structure in the Bighorn Mountains: Analysis of frequency dependence in shear wave splitting: Fall Meeting, AGU, San Francisco, CA, December 5-9, Abstract DI41A-2055.
Anderson, M. L., Thayer, D., Hornbuckle, J., Ufret-Alonso, T., Sheehan, A., Yeck, W., Solomon, M.*, Erslev, E., Siddoway, C., Miller, K., 2011, Anisotropy within the Bighorn Mountains region, northern Wyoming: Attempts to define cratonic mantle structure: EarthScope National Meeting, Austin, TX, May 17-20.
Collaborative Research: Structure of the Nazca slab and Sierras Pampeanas
NSF Geophysics Research Project #0738935, Cordoba, Argentina, 2008-present
My Ph.D. advisers and I still had many unanswered questions about the dynamics of subduction and mountain building in the Sierras Pampeanas and adjacent Andes Mountains in Argentina, even after our analysis of the CHARGE network data was complete (see Seismological Studies of the Central Chilean Subduction Zone below). While my advisers deployed a new, compact network of broadband seismometers over the zone of flat-slab subduction in western Argentina (SIEMBRA), Dr. Hersh Gilbert and I deployed 12 seismometers across the Sierras de Cordoba region (ESP) to extend the imaging power of the SIEMBRA network eastward. We had goals to image active seismicity in both the crust and mantle and crustal internal structure. Our goals included characterizing earthquake hazards and understanding how the mountains were formed, but it was also exciting to me that it was the first time a small, regional network had been installed in the Sierras de Cordoba, so we were the first to consistently characterize seismicity over the ranges. I think the most intriguing results from our work are that small crustal earthquakes are not spatially associated with the expected position of major range-bounding faults, the positions of which are easily identified at the surface from excellent outcrop evidence. We think these faults are therefore locked and building up strain to create large-magnitude future earthquakes. Instead, small earthquakes are grouped in a sub-horizontal cloud at 15-20 km depth, possibly indicating a broad zone of deformation (decollement or shear zone?) forming the root of the reverse faults that reach the surface. From subducting slab focal mechanisms and shear wave splitting, we also believe that there is a tear in the plate at the south end of the flattened zone and mantle is flowing through this gap.
Publications:
Lynner, C., Anderson, M. L., Portner, D. E., Beck, S. L., Gilber, H., 2017, Mantle flow through a tear in the Nazca slab inferred from shear wave splitting, Geophysical Research Letters, v. 44, no. 13, p. 6735-6742.
Richardson, T., Ridgway, K. D., Gilbert, H., Martino, R., Enkelmann, E., Anderson, M., Alvarado, P., 2013, Neogene tectonics of the Eastern Sierras Pampeanas, Argentina: Active intraplate deformation inboard of flat-slab subduction, Tectonics, v. 32, no. 3, p. 780-796.
Perarnau, M., Gilbert, H., Alvarado, P., Martino, R., Anderson, M., 2012, Crustal structure of the eastern Sierras Pampeanas of Argentina using high frequency local receiver functions, Tectonophysics, v. 580, p. 208-217.
Porter, R., Gilbert, H., Zandt, G., Beck, S., Warren, L., Calkins, J., Alvarado, P. Anderson, M., 2012, Shear-wave velocities in the Pampean flat-slab region from Rayleigh wave tomography: Implications for slab and upper mantle hydration, Journal of Geophysical Research, v. 117, no. B11301, doi:10.1029/2012JB009350.
Richardson, T., Gilbert, H., Anderson, M., Ridgway, K., 2011, Seismicity within the actively deforming Eastern Sierras Pampeanas, Argentina, Geophysical Journal International, doi: 10.1111/j.1365-246X.2011.05283.x.
Gans, C. R., Beck, S. L., Zandt, G., Gilbert, H., Alvarado, P, Anderson, M., Linkimer, L., 2011, Continental and oceanic crustal structure of the Pampean flat slab region, western Argentina, using receiver function analysis: new high-resolution results: Geophysical Journal International, v. 186, p. 45-58.
Select Abstracts:
Linkimer, L., Beck, S. L., Zandt, G., Alvarado, P. M., Anderson, M. L., Gilbert, H. J., Zhang, H., 2011, Lithospheric structure and shape of subducting Nazca plate in the Pampean flat slab region of Argentina: Fall Meeting, AGU, San Francisco, CA, December 5-9, Abstract DI44B-03.
Anderson, M. L., Linkimer, L., Olsen, K., Beck, S. L., Alvarado, P. M., Gilbert, H. J., 2010, Flat-slab dynamics: Deformation in the central Andean subducting slab: Fall Meeting, AGU, San Francisco, CA, December 13-17, Abstract DI42A-06.
INVITED Alvarado, P. M., Gilbert, H. J., Richardson, T. J., Anderson, M. L., Martino, R., 2010, Lithospheric deformation overlying a shallowly subducting slab: Insights from the Eastern Sierras Pampeanas seismic array: Fall Meeting, AGU, San Francisco, CA, December 13-17, Abstract T13D-03.
Olsen, K., Anderson, M. L., Linkimer, L., Gilbert, H. J., Beck, S. L., Zandt, G., Alvarado, P. M., 2010, Dynamics of flat slab subduction: Focal mechanisms, ridge buoyancy, and slab tear in central Arentina: Fall Meeting, AGU, San Francisco, CA, December 13-17, Abstract T11A-2047.
Dewey-Wood, F. D., Anderson, M. L., Gilbert, H. J., Alvarado, P. M., and Martino, R., 2009, Anisotropy and mantle flow in the eastern Sierras Pampeanas from shear wave splitting: Eos, v. 90, n. 52, Fall Meet. Suppl., Abstract DI41B-1813. Winner: Outstanding Student Presentation Award, Deep Earth Section.
Rift Geometry of the Sunshine Basin
Student-supported research projects, Colorado College, Colorado, 2007-2012
In my first 300-level class at CC, my enthusiastic students were up for collecting new gravity data in the Sunshine Valley within the San Luis basin, northern New Mexico. Researchers at the USGS studying potentially active faults accommodating the down dropping of the floor this sub-basin within the Rio Grande Rift were hoping we could help them trace these faults into the subsurface and identify faults with no surface expression. We collected a nice line of gravity measurements crossing the Rio Grande Gorge and put our heads together to develop a model of the subsurface that fits the observed gravity and aeromagnetic data for the region. This model supports the existence of 6-8 normal faults on either side of the Sunshine Valley sub-basin.
Publications:
Ruleman, C. A., Thompson, R. A., Shroba, R. S., Anderson, M. L., Dreneth, B., Rotzien, J., and Lyon, J., 2013, Late Miocene-Pleistocene evolution of a Rio Grande rift sub-basin, Sunshine Valley-Costilla Plain, San Luis Basin, New Mexico and Colorado: New Perspectives on the Rio Grande rift: From Tectonics to Groundwater, GSA Special Paper, v. 494, p.47-73, doi:10.1130/2013.2494(03).
Technology Assistance with Implementation and Operation of Transportable Array Element of USArray and EarthScope
Student-supported siting of USArray seismic stations in Colorado, 2007
Advised teams of students from Colorado College and other Colorado universities finding sites for the Colorado portion of the USArray seismic network.
Southern California GPS Network Development
Collaborative project with Rick Bennett at the University of Arizona, 2004-2008
This project tackled a deceptively simple question: where does the Eastern California shear zone start? The ECSZ is a subsidiary zone of deformation to the San Andreas Fault zone and traverses the Mojave desert through to the eastern side of the Sierra Nevada Mountains. It helps accommodate some of the northward sliding of the Pacific plate relative to the North American plate. Of course, the ECSZ starts at the San Andreas fault, but we weren’t sure exactly where along the fault it branches off. Lucky for me, it was most likely that the ECSZ meets the San Andreas somewhere within Joshua Tree National Park, one of my favorite places on the planet. I worked with Rick Bennett and his students/postdocs to permit and construct a campaign GPS network within the park to answer this question. Our graduate student Josh Spinler constructed block models, constrained by known and expected fault locations (from geology and gravity map interpretations), to test against our data. We discovered that right-lateral strike-slip motion on the ECSZ within the park region is accommodated by a combination of motions: 1) clockwise rotation of east-trending crustal blocks bounded north and south by left-lateral faults and 2) a small NNW-trending fault within the extreme western part of the park that originated a M 6.1 earthquake in 1992.
Publications:
Spinler, J. C., Bennett, R. A., Anderson, M. L., McGill, S. F., Hreinsdottir, S., Mcallister, A., 2010, Present-day strain accumulation and slip rates associated with southern San Andreas and eastern California shear zone faults, Journal of Geophysical Research, v. 115, B11407, doi:10.1029/2010JB007424.
Seismological Studies of the Central Chilean Subduction Zone
Graduate Research Project, University of Arizona, Tucson, AZ, 2000-2005
The central Chilean subduction zone, along the Andean spine of South America has an unusual geometry of subduction. The Nazca plate, underlying the Pacific Ocean subducts eastward under the continent and then flattens out at a depth of ~100 km before sinking deeper into the mantle. As a graduate student, I became enamored with this strange tectonic system. What dynamics are present that make this kind of subducting slab contortion possible? In an enigmatic twist, the region where the “flat-slab subduction” happens is also occupied by basement arches at the surface, the Sierras Pampeanas (see Collaborative Research: Formation of basement-involved foreland arches above for more about these unusual types of mountain ranges). I wondered if there was a dynamic link between the subduction and the unusual ranges–is the process of their formation connected? Many other researchers wonder this too, and though we don’t have definitive solutions yet, these questions formed the starting point for over a decade of research into flat subduction and basement arches modern and ancient. For my Ph.D., I assisted with the maintenance of a broadband seismic network (CHARGE) deployed over the Andes Mountains and adjacent Sierras Pampeanas, western Argentina and Chile. I used this data to compute high quality hypocenters and focal mechanisms for earthquakes originating from the subducting plate in order to carefully map its shape and its response to the stresses that contort it. I also computed shear wave splitting parameters from waves traversing the region to understand mantle deformation and its interaction with the subducting plate. In conjunction with later work (see Collaborative Research: Structure of the Nazca slab and Sierras Pampeanas above), the data supports the hypothesis that a subducted oceanic hot-spot track (the Juan Fernandez ridge) is helping to buoy the subducting plate and stabilize it in the upper mantle.
We also believe that there is a tear in the plate at the south end of the flattened zone and mantle is flowing through this gap.
Publications:
MacDougall, J. G., Fischer, K. M., Anderson, M. L., 2013, Seismic anisotropy above and below the subducting Nazca lithosphere in southern South America, Journal of Geophysical Research, v. 117, no. B12306, doi: 10.1029/2012JB009538.
Wagner, L., Anderson, M., Beck, S., Zandt, G., 2008, Seismic evidence for orthopyroxene enrichment in the continental lithosphere: Geology, v. 36, no. 12, p. 935-938.
Anderson, M. L., Alvarado, P., Zandt, G., Beck, S., 2007, Geometry and brittle deformation of the subducting Nazca plate, central Chile and Argentina: Geophysical Journal International, v. 171, p. 419-434.
Anderson, M. L., Zandt, G., Triep, E., Fouch, M., Beck, S., 2004, Anisotropy and mantle flow in the Chile-Argentina subduction zone from shear wave splitting analysis: Geophysical Research Letters, 31, L23608, doi:10.1029/2004GL020906.
Assessing Earthquake Location Error
Lawrence Livermore National Laboratory, Livermore, CA, 2003
Seismologists at the U.S. national labs are busy improving our ability to verify nuclear test locations and sizes around the globe using seismological records. I spent the summer in 2003 working with lab scientists to investigate questions I had about the accuracy of seismic event locations. In particular, I evaluated a code that can locate other events relative to one or several events of known location. I found that no more than 5-10 known events are necessary to effectively constrain the location of other events in the region. I also confirmed what others had hypothesized about earthquake location: the difference between the velocity model you assume and reality maps into seismic event mislocation, and can even sometimes artificially lower the main metric we have to test fit of the location to the data: RMS error. Therefore RMS error is a poor metric for evaluating the accuracy of seismic event locations.
Anderson, M. L., Myers, S. C., 2010, Assessment of regional-distance location calibration using a multiple event location algorithm: Bulletin of the Seismological Society of America, v. 100, no. 2, p. 868-875.
Structure of the San Jacinto Fault Zone and San Bernardino Basin
U.S. Geological Survey, Menlo Park, CA, 1998-2000
I was so lucky to land an internship at the USGS office in Menlo Park, California after college. I was really interested in earthquakes, tectonics, and what the heck is in the lower crust, which we can never visit in person. We can understand all these pieces and processes in the earth using geophysics. I had never studied geophysics in school, but my mentor Bob Jachens took a gamble on me, and it paid off! After the first two weeks measuring rock physical property measurements in a dusty lab, the first field foray of my internship was scheduled and I was off and running. I was trained in the mapping and interpretation of potential field geophysical data and also in field gravity data collection, assisted a couple of people with their field work, then got my second independent research project of my life: imaging active faults within the San Jacinto fault zone in southern California. The original goal was finding a strand of the fault zone running through Rialto for ground water modeling, but I collected enough data to create a refined gravity map for a large structure next door: the San Bernardino basin. This is a steep-sided pull-apart basin that will enhance ground shaking in the San Bernardino urban area during a major earthquake on the San Andreas or associated faults. From my new map, I created new estimates of the depth and shape of the basin that was eventually incorporated into the SCEC crustal model used for major earthquake simulation in southern California. As for geophysics, I was hooked.
Publications:
Anderson, M., Matti, J., Jachens, R., 2004, Structural model of the San Bernardino Basin, California from analysis of gravity, aeromagnetic, and seismicity data: Journal of Geophysical Research, v. 109, B04404.
Stephenson, W. J., Odum, J. K., Williams, R. A., Anderson, M. L., 2002, Delineation of faulting and basin geometry beneath urbanized San Bernardino Valley, California, from seismic reflection and gravity data: Bulletin of the Seismological Society of America, v. 96, no. 6, p. 2504-2520.
Stratigraphy of the Crandall Conglomerate
Undergraduate Senior Thesis Research Project, Keck Consortium Project, Greater Yellowstone Area, Wyoming, 1997-1998
Characterized stratigraphy of the Crandall conglomerate and interpreted the paleotectonic setting.
Structure of the Appalachian Mountains
Keck Consortium Research Project, Williams College, Massachusetts, 1996-1997
Mapped surficial geology and made cross sections for an area of the Berkshire Mountains.
