news


June 29, 2012: A "Skyquake" occurred at 12:45 PM today that was felt in many parts of the county. I felt it in San Marcos and was contacted by the press for a statement. The CBS story included a ray tracing figure shown here from the April 13 boom. CBS, NBC, FOX

G2S Update: I had to take this website offline due to a reconfiguration of the webserver. Apr. 2012: Recent progress on the G2S project has led to this new website that shows the last 24 hours of global stratospheric wind evolution, and how that conspires with temperature to influence the potential for stratospheric ducting. The Cratio is the ratio of the effective sound speed in the stratosphere to that at the surface. Values of CRatio > 1 (warm colors) mean the ducting potential is great for broadband infrasound in the direction of the mean stratospheric wind (black vectors). Values less than 1 (cool colors) mean stratospheric ducting will be strongly frequency dependent (generally only happening at lower frequencies below 1 Hz). White squares are the IMS infrasonic arrays. The G2S system is installed on at least three institutions: UCSD, Univ. of Mississippi, and the Naval Research Lab (via Doug Drog, creator of 'G2S').

Apr. 22, 2012: There was a large "boom" felt in Northern California. The infrasound radiated from this event suggests the event was a mini-van sized meteor that exploded above the Earth's surface. Several of my arrays recorded this event. My analysis of SMIAR, a 9-element array near Temecula, and IS57 (PFO) shows a 15-minute long wavetrain coming from the northwest, pointing to central California. This event was also recorded by at least one OFIS sensor in Chico, California. That sensor provides a better recording of the source function since it was much closer to the event (1-5Hz, raw). Elizabeth Silber is analyzing this event in more detail.


Apr. 13, 2012: There was a large "boom" felt in San Diego. My preliminary analysis is presented here here.


Dec. 23, 2011: "Acoustic Ray Tracer, 2D" or "ART2D" has been released. Check out the link here.

stacks

Dec. 13, 2011: My USArray work has been published. Many thanks to JGR Solid Earth and two anonymous reviewers for helping this go to press so quickly. Click here for the paper.

microbaroms

Jan. 13, 2011: UCSD infrasound arrays are detecting microbaroms coming from the eastern Pacific Ocean. CLICK HERE FOR AN OCTOBER 2011 UPDATE or HERE FOR A JANUARY 2012 UPDATE. Each of the arrays comprise several infrasonic microphones separated by several hundred meters. Pressure signals generated just above the ocean surface, likely from beating due to interfering opposing swells, travel great distances through the atmosphere. These signals are detected by each of the sensors in the arrays. Array processing identifies the direction from which the signals originated (back azimuth). We project these back azimuths outward from these arrays to form an intersecting back azimuth density color map, where reds indicate high densities. The color map has been converted to signal-to-noise ratio. The black contour is the statistical 95% confidence region for a model where there is only one source to explain all the detections at the arrays. The OFIS CHIAR array provided results that were consistent with those of the other arrays. This is the first time that the OFIS technology has been used for infrasound source physics research. Click here for a movie.

Kris Walker

Assoc. Research Geophysicist
Inst. of Geophysics and Planetary Physics
Scripps Institution of Oceanography
University of California, San Diego

Contact info

858-534-0126 (o)
650-814-4452 (c)
858-534-6354 (f)
Revelle 2000, Rm. 2110
kwalker@ucsd.edu
http://sail.ucsd.edu/~kwalker/

US Mail:
9500 Gilman Ave., MC 0225
La Jolla, CA 92093-0225

FedEx/UPS:
8785 Biological Grade, Room 4114
La Jolla, CA 92037

Who Am I?


I'm a computational geophysicist with expertise in reflection seismology, earthquake seismology, explosion seismology, acoustics, potential fields, and interferometric sensing. My passion is using computers to solve large problems. I typically do this in the form of software development for the purposes of multi-dimensional array processing of massive data sets, data modeling, data mining, and uncertainty quantification. I'm experienced in project management from the stages of proposal writing to the publication of results. I've published 23 refereed papers and more than 60 abstracts/reports. My diverse research background has provided me with the experience necessary to efficiently cross disciplines, as well as a knowledge base from which I routinely adapt and improve techniques to solve problems in emerging fields.

Education

2004: Stanford University, Ph.D., Teleseismic Seismology (Thesis)
2000: Stanford University – M.S., Active-source Seismology
1998: University of Delaware – B.S. w/ Distinction, Geophysics, Cum Laude (Thesis, Plates 1/2, Plates 3/4, Plate 5, Plates 6/7, Plate 8) )

Professional Experience

  • 2013-current: Assoc. Research Geophysicist, IGPP, Scripps, Univ. of California, San Diego
  • 2009-13: Asst. Project Scientist, IGPP, Scripps, Univ. of California, San Diego
  • 2005-06: Cecil & Ida Green Scholar, IGPP, Scripps, Univ. of California, San Diego
  • 2004-09: Postdoctoral Researcher, IGPP, Scripps, Univ. of California, San Diego

Recent Publications

Walker, K. T., A. Le Pichon, T. S. Kim, C. de Groot-Hedlin, Il.-Y. Che, and M. Garcés (2013), An analysis of ground shaking and transmission loss from infrasound generated by the 2011 Tohoku earthquake, J. Geophys. Res. Atmos., 118, doi:10.1002/2013JD020187. [web, pdf]


de Groot-Hedlin, C., Hedlin, M., and Walker, K. T., 2013, Detection of gravity waves across the USArray: A case study, Earth Planet. Sci. Lett., doi:10.1016/j.epsl.2013.06.042. [web, pdf]


DeWolf, S., Walker, K. T., Zumberge, M. A., and Denis, S., 2013, Efficacy of spatial averaging of infrasonic pressure in varying wind speeds, J. Acoust. Soc. Am., 133, 3739-3750, doi:10.1121/1.4803891. [web, pdf]


Walker, K. T., 2012, Evaluating the opposing-wave interaction hypothesis for the generation of microbaroms in the eastern North Pacific, J. Geophys. Res, 117, C12016, doi:10.1029/2012JC008409. [web, pdf]


Hedlin, M., and Walker, K., A study of infrasonic anisotropy and multipathing in the atmosphere using seismic networks, Phil. Trans. R. Soc. A , 371:20110542; doi:10.1098/rsta.2011.0542. [web, pdf]


Hedlin, M.A.H., Walker, K., Drob, D. and de Groot-Hedlin, C.D., 2012, Infrasound: Connecting the Solid Earth, Oceans and Atmosphere, Annu. Rev. Earth Planet. Sci., 40, 327-354. [web, pdf]


Walker, K.T., Shelby, R., Hedlin, M., de Groot-Hedlin, C., and Vernon, F., 2011, Western U.S. Infrasonic Catalog: Illuminating infrasonic hot spots with the USArray, J. Geophys. Res., 116, B12305, doi:10.1029/2011JB008579. [web, pdf]


de Groot-Hedlin, C., Hedlin, M., and Walker, K., 2011, Finite difference synthesis of infrasound propagation through a windy, viscous atmosphere: application to a bolide explosion detected by seismic networks, Geophys. J. Int., doi: 10.1111/j.1365-246X.2010.04925.x. [web]