Publications

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2016
Wu, Y, Smith SGL, Rottman JW, Broutman D, Minster JBH.  2016.  The propagation of tsunami-generated acoustic-gravity waves in the atmosphere. Journal of the Atmospheric Sciences. 73:3025-3036.   10.1175/jas-d-15-0255.1   AbstractWebsite

Tsunami-generated acoustic-gravity waves have been observed to propagate in the atmosphere up to the ionosphere, where they have an impact on the total electron content. The authors simulate numerically the propagation of two-dimensional linear acoustic-gravity waves in an atmosphere with vertically varying stratification and horizontal background winds. The authors' goal is to compare the difference in how much energy reaches the lower ionosphere up to an altitude of 180 km, where the atmosphere is assumed to be anelastic or fully compressible. The authors consider three specific atmospheric cases: a uniformly stratified atmosphere without winds, an idealized case with a wind jet, and a realistic case with an atmospheric profile corresponding to the 2004 Sumatra tsunami. Results show that for the last two cases, the number and height of turning points are different for the anelastic and compressible assumptions, and the net result is that compressibility enhances the total transmission of energy through the whole atmosphere.

2012
Borsa, A, Minster JB.  2012.  Rapid Determination of Near-Fault Earthquake Deformation Using Differential LiDAR. Bulletin of the Seismological Society of America. 102:1335-1347.   10.1785/0120110159   AbstractWebsite

Improved near-field measurements of earthquake slip and deformation patterns have the potential for expanding our understanding of fault behavior and the relationship of active faulting to topography. Current techniques for obtaining these measurements-including field observation, Global Navigation Satellite Systems displacement estimation, and optical or radar remote sensing-have limitations that can be mitigated by the inclusion of results from differential airborne Light Detection and Ranging (LiDAR) analysis of the rupture zone. The 2005 airborne LiDAR survey of the southern San Andreas, San Jacinto, and Banning faults (the B4 survey) mapped 1100 km of the most seismically active fault systems in southern California for the purpose of providing a baseline for determining slip from a future earthquake. We used the B4 survey to develop a processing algorithm that yields rapid estimates of near-fault ground deformation using simultaneous cross correlation of both topography and backscatter intensity from pre-earthquake and simulated postearthquake LiDAR datasets. We show robust recovery of the direction and magnitude of an applied synthetic slip of 5 m in the horizontal and 0.5 m in the vertical within our area of study, with clear discrimination between areas with and without applied slip. We also successfully recovered more complex deformation from a modeled fault stepover in the same study area. Our results indicate that we should be able to recover slip to accuracies of better than 20 cm in the horizontal and 1 cm in the vertical, at a spatial resolution of <= 15 m for LiDAR datasets with sample densities as low as 0: 5 points/m(2).

2011
Nesbit, J, Norman C, Konstantinov I, Stefanov Y, Kovalevsky A, Voronin Y, Lee I, Ahn M, Marcotte E, Rhee SY, Heras J, Elliot K, Fayyaz M, Crnokrak P, Darling SB, Sibener SJ, Belliveau RR, Hoffman KL, Wood RJ, Pope D, Dick G, Bradley S, Kelley S, Chourasia A, McQuinn E, Minster B, Schulze J, Cox TJ, Berry D, Ellisman M, Tetaz F.  2011.  2010 Visualization Challenge. Science. 331:847-856.   10.1126/science.331.6019.847   Website
2010
Ely, GP, Day SM, Minster JB.  2010.  Dynamic Rupture Models for the Southern San Andreas Fault. Bulletin of the Seismological Society of America. 100:131-150.   10.1785/0120090187   AbstractWebsite

Dynamic rupture, and resultant ground motions up to 0.25 Hz, are simulated for an M(w) 7.6 earthquake on the southern San Andreas fault. Spontaneous rupture is modeled with slip-weakening friction, and 3D viscoelastic wave solutions are computed with a support-operator numerical method. The initial traction model is derived from inversions of the M(w) 7.3 1992 Landers strong ground-motion records, and borrows heavily from that used for the TeraShake2 simulations by Olsen et al. (2008). Heterogeneity in the traction model leads to focusing of the rupture front, and the focusing produces cases of supershear rupture velocity in asperities (areas of high initial traction), as well as cases of high peak slip rate and cohesive zone contraction in antiasperities. Separate solutions are computed for version 3.0 and 4.0, respectively, of the Southern California Earthquake Center Community Velocity Model (SCEC-CVM). We also compare the case of a flat ground surface (a common simplification made for finite-difference simulations) to the case of the ground surface conformed to regional topography. The overall distribution of simulated ground motion intensity is consistent with that derived from the empirical model of Campbell and Bozorgnia (2008), in the sense that the bulk of simulated pseudospectral velocity (PSV) values are within the 68% confidence intervals of the empirical model. Simulated PSVs corresponding to low probability in the empirical model are principally associated with basin waveguide and directivity effects. An important example, first identified by the TeraShake1 simulations (Olsen et al., 2006), is the stronger than expected ground motions at the site of Montebello due to a basin wave-guide effect. We find that this effect is lessened for version 4.0 of the SCEC-CVM, relative to version 3.0, due to a shallower model for the Chino basin.

2009
Ely, GP, Day SM, Minster JB.  2009.  A support-operator method for 3-D rupture dynamics. Geophysical Journal International. 177:1140-1150.   10.1111/j.1365-246X.2009.04117.x   AbstractWebsite

We present a numerical method to simulate spontaneous shear crack propagation within a heterogeneous, 3-D, viscoelastic medium. Wave motions are computed on a logically rectangular hexahedral mesh, using the generalized finite-difference method of Support Operators (SOM). This approach enables modelling of non-planar surfaces and non-planar fault ruptures. Our implementation, the Support Operator Rupture Dynamics (SORD) code, is highly scalable, enabling large-scale, multiprocessors calculations. The fault surface is modelled by coupled double nodes, where rupture occurs as dictated by the local stress conditions and a frictional failure law. The method successfully performs test problems developed for the Southern California Earthquake Center (SCEC)/U.S. Geological Survey (USGS) dynamic earthquake rupture code validation exercise, showing good agreement with semi-analytical boundary integral method results. We undertake further dynamic rupture tests to quantify numerical errors introduced by shear deformations to the hexahedral mesh. We generate a family of meshes distorted by simple shearing, in the along-strike direction, up to a maximum of 73 degrees. For SCEC/USGS validation problem number 3, grid-induced errors increase with mesh shear angle, with the logarithm of error approximately proportional to angle over the range tested. At 73 degrees, firms misfits are about 10 per cent for peak slip rate, and 0.5 per cent for both rupture time and total slip, indicating that the method (which, up to now, we have applied mainly to near-vertical strike-slip faulting) is also capable of handling geometries appropriate to low-angle surface-rupturing thrust earthquakes. Additionally, we demonstrate non-planar rupture effects, by modifying the test geometry to include, respectively, cylindrical curvature and sharp kinks.

Cui, YF, Moore R, Olsen K, Chourasia A, Maechling P, Minster B, Day S, Hu YF, Zhu J, Jordan T.  2009.  Toward petascale earthquake simulations. Acta Geotechnica. 4:79-93.   10.1007/s11440-008-0055-2   AbstractWebsite

Earthquakes are among the most complex terrestrial phenomena, and modeling of earthquake dynamics is one of the most challenging computational problems in science. Computational capabilities have advanced to a state where we can perform wavefield simulations for realistic three-dimensional earth models, and gain more insights into the earthquakes that threaten California and many areas of the world. The Southern California Earthquake Center initiated a major earthquake research program called TeraShake to perform physics-based numerical simulations of earthquake processes for large geographical regions, at high resolution, and for high frequencies. For a large scale simulation such as TeraShake, optimization problems tend to emerge that are not significant in smaller scale simulations. This involves both large parallel computation and also massive data management and visualization coordination. In this paper, we describe how we performed single-processor optimization of the TeraShake AWM application, optimization of the I/O handling, and optimization of initialization. We also look at the challenges presented by run-time data archive management and visualization. The improvements made to the TeraShake AWM code enabled execution on the 40k IBM Blue Gene processors and have created a community code that can be used by seismologists to perform petascale earthquake simulations.

2008
Borsa, AA, Bills BG, Minster JB.  2008.  Modeling the topography of the salar de Uyuni, Bolivia, as an equipotential surface of Earth's gravity field. Journal of Geophysical Research-Solid Earth. 113   10.1029/2007jb005445   AbstractWebsite

The salar de Uyuni is a massive dry salt lake that lies at the lowest point of an internal drainage basin in the Bolivain Altiplano. A kinematic GPS survey of the salar in September 2002 found a topographic range of only 80 cm over a 54 x 45 km area and subtle surface features that appeared to correlate with mapped gravity. In order to confirm the correlation between topography and gravity/geopotential, we use local gravity measurements and the EGM96 global geopotential model to construct a centimeter-level equipotential surface corresponding to the elevation of the salar. Our comparison of GPS survey elevations with equipotential surface estimate shows that 63% of the variance of the GPS elevations can be explained by equipotential surface undulations (and long-wavelength error) in the EGM96 model alone, with an additional 30% explained by the shorter-wavelength equipotential surface derived from local gravity. In order to establish a physical connection between topography and the geopotential, we also develop and test a simple surface process model that redistributes salt via the dissolution, transport, and redeposition of salt by precipitated water. Forcing within the model pushes the system to evolve toward constant water depth, with the salt surface approximating the shape of the local equipotential surface. Since the model removes almost all topographic relief with respect to the equipotential surface within a matter of decades, it appears that observed (similar to 5 cm amplitude, similar to 5 km wavelength) residual topography is actively maintained by a process independent of gravity-driven fluid flow.

Olsen, KB, Day SM, Minster JB, Cui Y, Chourasia A, Okaya D, Maechling P, Jordan T.  2008.  TeraShake2: Spontaneous rupture simulations of M(w) 7.7 earthquakes on the southern San Andreas fault. Bulletin of the Seismological Society of America. 98:1162-1185.   10.1785/0120070148   AbstractWebsite

Previous numerical simulations (TeraShake1) of large (M(w) 7.7) southern San Andreas fault earthquakes predicted localized areas of strong amplification in the Los Angeles area associated with directivity and wave-guide effects from northwestward-propagating rupture scenarios. The TeraShake1 source was derived from inversions of the 2002 M(w) 7.9 Denali, Alaska, earthquake. That source was relatively smooth in its slip distribution and rupture characteristics, owing both to resolution limits of the inversions and simplifications imposed by the kinematic parameterization. New simulations (TeraShake2), with a more complex source derived from spontaneous rupture modeling with small-scale stress-drop heterogeneity, predict a similar spatial pattern of peak ground velocity (PGV), but with the PGV extremes decreased by factors of 2-3 relative to TeraShake1. The TeraShake2 source excites a less coherent wave field, with reduced along-strike directivity accompanied by streaks of elevated ground motion extending away from the fault trace. The source complexity entails abrupt changes in the direction and speed of rupture correlated to changes in slip-velocity amplitude and waveform, features that might prove challenging to capture in a purely kinematic parameterization. Despite the reduced PGV extremes, northwest-rupturing TeraShake2 simulations still predict entrainment by basin structure of a strong directivity pulse, with PGVs in Los Angeles and San Gabriel basins that are much higher than predicted by empirical methods. Significant areas of those basins have predicted PGV above the 2% probability of exceedance (POE) level relative to current attenuation relationships (even when the latter includes a site term to account for local sediment depth), and wave-guide focusing produces localized areas with PGV at roughly 0.1%-0.2% POE (about a factor of 4.5 above the median). In contrast, at rock sites in the 0-100-km distance range, the median TeraShake2 PGVs are in very close agreement with the median empirical prediction, and extremes nowhere reach the 2% POE level. The rock-site agreement lends credibility to some of our source-modeling assumptions, including overall stress-drop level and the manner in which we assigned dynamic parameters to represent the mechanical weakness of near-surface material. Future efforts should focus on validating and refining these findings, assessing their probabilities of occurrence relative to alternative rupture scenarios for the southern San Andreas fault, and incorporating them into seismic hazard estimation for southern California.

Bassis, JN, Fricker HA, Coleman R, Minster JB.  2008.  An investigation into the forces that drive ice-shelf rift propagation on the Amery Ice Shelf, East Antarctica. Journal of Glaciology. 54:17-27.   10.3189/002214308784409116   AbstractWebsite

For three field seasons (2002/03, 2004/05, 2005/06) we have deployed a network of GPS receivers and seismometers around the tip of a propagating rift on the Amery Ice Shelf, East Antarctica. During these campaigns we detected seven bursts of episodic rift propagation. To determine whether these rift propagation events were triggered by short-term environmental forcings, we analyzed simultaneous ancillary data such as wind speeds, tidal amplitudes and sea-ice fraction (a proxy variable for ocean swell). We find that none of these environmental forcings, separately or together, correlated with rift propagation. This apparent insensitivity of ice-shelf rift propagation to short-term environmental forcings leads us to suggest that the rifting process is primarily driven by the internal glaciological stress. Our hypothesis is supported by order-of-magnitude calculations that the glaciological stress is the dominant term in the force balance. However, our calculations also indicate that as the ice shelf thins or the rift system matures and iceberg detachment becomes imminent, short-term stresses due to winds and ocean swell may become more important.

2007
Chourasia, A, Cutchin S, Cui YF, Moore RW, Olsen K, Day SM, Minster JB, Maechling P, Jordan TH.  2007.  Visual insights into high-resolution earthquake simulations. Ieee Computer Graphics and Applications. 27:28-34.   10.1109/mcg.2007.138   Website
Ely, GP, Day SM, Minster JB.  2007.  A support-operator method for viscoelastic wave modelling in 3-D heterogeneous media. Geophysical Journal International. 172:331-344.   10.1111/j.1365-246X.2007.03633.x   AbstractWebsite

We apply the method of support operators (SOM) to solve the 3-D, viscoelastic equations of motion for use in earthquake simulations. SOM is a generalized finite-difference method that can utilize meshes of arbitrary structure and incorporate irregular geometry. Our implementation uses a 3-D, logically rectangular, hexahedral mesh. Calculations are second-order in space and time. A correction term is employed for suppression of spurious zero-energy modes (hourglass oscillations). We develop a free surface boundary condition, and an absorbing boundary condition using the method of perfectly matched layers (PML). Numerical tests using a layered material model in a highly deformed mesh show good agreement with the frequency-wavenumber method, for resolutions greater than 10 nodes per wavelength. We also test a vertically incident P wave on a semi-circular canyon, for which results match boundary integral solutions at resolutions greater that 20 nodes per wavelength. We also demonstrate excellent parallel scalability of our code.

Borsa, AA, Fricker HA, Bills BG, Minster JB, Carabajal CC, Quinn KJ.  2007.  Topography of the salar de Uyuni, Bolivia from kinematic GPS. Geophysical Journal International. 172:31-40.   10.1111/j.1365-246X.2007.03604.x   AbstractWebsite

The salar de Uyuni in the Bolivian Andes is the largest salt flat on Earth, exhibiting less than 1 m of vertical relief over an area of 9000 km(2). We report on a kinematic Global Positioning System (GPS) survey of a 45-by-54 km area in the eastern salar, conducted in September 2002 to provide ground truth for the Ice Cloud and land Elevation Satellite (ICESat) mission. GPS post-processing included corrections for long-period GPS noise that significantly improved survey accuracy. We fit corrected GPS trajectories with 2-D Fourier basis functions, from which we created a digital elevation model (DEM) of the surface whose absolute accuracy we estimate to be at least 2.2 cm RMSE. With over two magnitudes better vertical resolution than the Shuttle Radar Topography Mission data, this DEM reveals decimetre-level topography that is completely absent in other topographic data sets. Longer wavelengths in the DEM correlate well with mapped gravity, suggesting a connection between broad-scale salar topography and the geoid similar to that seen over the oceans.

Borsa, AA, Minster JB, Bills BG, Fricker HA.  2007.  Modeling long-period noise in kinematic GPS applications. Journal of Geodesy. 81:157-170.   10.1007/s00190-006-0097-x   AbstractWebsite

We develop and test an algorithm for modeling and removing elevation error in kinematic GPS trajectories in the context of a kinematic GPS survey of the salar de Uyuni, Bolivia. Noise in the kinematic trajectory ranges over 15 cm and is highly autocorrelated, resulting in significant contamination of the topographic signal. We solve for a noise model using crossover differences at trajectory intersections as constraints in a least-squares inversion. Validation of the model using multiple realizations of synthetic/simulated noise shows an average decrease in root-mean-square-error (RMSE) by a factor of four. Applying the model to data from the salar de Uyuni survey, we find that crossover differences drop by a factor of eight (from an RMSE of 5.6 to 0.7 cm), and previously obscured topographic features are revealed in a plan view of the corrected trajectory. We believe that this algorithm can be successfully adapted to other survey methods that employ kinematic GPS for positioning.

Bassis, JN, Fricker HA, Coleman R, Bock Y, Behrens J, Darnell D, Okal M, Minster JB.  2007.  Seismicity and deformation associated with ice-shelf rift propagation. Journal of Glaciology. 53:523-536.   10.3189/002214307784409207   AbstractWebsite

Previous observations have shown that rift propagation on the Amery Ice Shelf (AIS), East Antarctica, is episodic, occurring in bursts of several hours with typical recurrence times of several weeks. Propagation events were deduced from seismic swarms (detected with seismometers) concurrent with rapid rift widening (detected with GPS receivers). In this study, we extend these results by deploying seismometers and GPS receivers in a dense network around the tip of a propagating rift on the AIS over three field seasons (2002/03, 2004/05 and 2005/06). The pattern of seismic event locations shows that icequakes cluster along the rift axis, extending several kilometers back from where the rift tip was visible in the field. Patterns of icequake event locations also appear aligned with the ice-shelf flow direction, along transverse-to-rift crevasses. However, we found some key differences in the seismicity between field seasons. Both the number of swarms and the number of events within each swarm decreased during the final field season. The timing of the slowdown closely corresponds to the rift tip entering a suture zone, formed where two ice streams merge upstream. Beneath the suture zone lies a thick band of marine ice. We propose two hypotheses for the observed slowdown: (1) defects within the ice in the suture zone cause a reduction in stress concentration ahead of the rift tip; (2) increased marine ice thickness in the rift path slows propagation. We show that the size-frequency distribution of icequakes approximately follows a power law, similar to the well-known Gutenberg-Richter law for earthquakes. However, large icequakes are not preceded by foreshocks nor are they followed by aftershocks. Thus rift-related seismicity differs from the classic foreshock and aftershock distribution that is characteristic of large earth quakes.

2006
Ragona, D, Minster B, Rockwell T, Jussila J.  2006.  Field imaging spectroscopy: A new methodology to assist the description, interpretation, and archiving of paleoseismological information from faulted exposures. Journal of Geophysical Research-Solid Earth. 111   10.1029/2006jb004267   AbstractWebsite

[1] We present a new methodology to acquire, interpret, and store stratigraphic and structural information from paleoseismic exposures. For this study we employed portable hyperspectral cameras to acquire field-based visible near-infrared (VNIR) and short-wave infrared (SWIR) high spatial/spectral resolution images. We first analyzed 400 small sediments cores using a hand-held, single-pixel spectrometer (VNIR-SWIR) to determine the feasibility of the method and to assess its potential problems. We then acquired high-spatial resolution ( submillimeter) spectral data of a large sample ( 60 x 60 cm) and four cores (7.5 x 60 cm) of faulted sediments from a paleoseismic excavation using portable push broom AISA hyperspectral scanner. These data, which contain 244 ( VNIR) and 245 ( SWIR) narrow contiguous spectral bands between 400 and 1000 and 960 to 2403 nm, respectively, were processed to obtain the reflectance spectra at each pixel. In this study we are focusing on the analysis of the short-wave infrared data sets ( SWIR). The SWIR data were transformed into relative reflectance and geometrically corrected and processed with well-known imaging processing algorithms. Selected spectra were then used to create false color composite images that best display the faulted stratigraphy. We compared the hyperspectral images to those recorded by a digital camera as well as directly to the field sample and show that the reflectance properties of the materials in the SWIR region cannot only enhance the visualization of the sedimentary layers and other features that are not obvious to the human eye but can also make visible many detailed features that were not visible in the digital photography. This new data collection and interpretation methodology, herein termed field imaging spectroscopy, makes available, for the first time, a tool to quantitatively analyze paleoseismic and stratigraphic information. In addition, hyperspectral data sets in the visible short-wave infrared spectral range provide a better alternative for data storage. The reflectance spectra at each pixel of the images provide unbiased compositional information that can be processed in a variety of ways to assist with the interpretation of stratigraphy and structure at a site.

Olsen, KB, Day SM, Minster JB, Cui Y, Chourasia A, Faerman M, Moore R, Maechling P, Jordan T.  2006.  Strong shaking in Los Angeles expected from southern San Andreas earthquake. Geophysical Research Letters. 33   10.1029/2005gl025472   AbstractWebsite

The southernmost San Andreas fault has a high probability of rupturing in a large ( greater than magnitude 7.5) earthquake sometime during the next few decades. New simulations show that the chain of sedimentary basins between San Bernardino and downtown Los Angeles form an effective waveguide that channels Love waves along the southern edge of the San Bernardino and San Gabriel Mountains. Earthquake scenarios with northward rupture, in which the guided wave is efficiently excited, produce unusually high long-period ground motions over much of the greater Los Angeles region, including intense, localized amplitude modulations arising from variations in waveguide cross-section.

2005
Fricker, HA, Borsa A, Minster B, Carabajal C, Quinn K, Bills B.  2005.  Assessment of ICESat performance at the Salar de Uyuni, Bolivia. Geophysical Research Letters. 32   10.1029/2005gl023423   AbstractWebsite

The primary goal of the Ice, Cloud and land Elevation Satellite (ICESat) mission is ice sheet elevation change detection. Confirmation that ICESat is achieving its stated scientific requirement of detecting spatially-averaged changes as small as 1.5 cm/year requires continual assessment of ICESat-derived elevations throughout the mission. We use a GPS-derived digital elevation model (DEM) of the salar de Uyuni, Bolivia for this purpose. Using all twelve ICESat passes over the salar survey area acquired to date, we show that the accuracy of ICESat-derived elevations is impacted by environmental effects (e.g., forward scattering and surface reflectance) and instrument effects (e.g., pointing biases, detector saturation, and variations in transmitted laser energy). We estimate that under optimal conditions at the salar de Uyuni, ICESat-derived elevations have an absolute accuracy of <2 cm and precision of <3 cm.

Bassis, JN, Coleman R, Fricker HA, Minster JB.  2005.  Episodic propagation of a rift on the Amery Ice Shelf, East Antarctica. Geophysical Research Letters. 32   10.1029/2004gl022048   AbstractWebsite

We investigate ice shelf rift propagation using a combination of GPS and seismic measurements near the tip of an active rift in the Amery Ice Shelf. These measurements reveal that propagation occurs in episodic bursts, which were identified based on swarms of seismicity accompanied by rapid rift widening. The bursts last approximately 4 hours and are separated by 10-24 days. In between bursts, the rift widens at a rate comparable to that of ice shelf spreading. Comparison of automatic weather station data and tidal amplitudes show that the propagation bursts are not directly triggered by winds or tides, suggesting that rift propagation is driven by the background glaciological stress in the ice shelf. We show that the ice debris that partly fills the rift may play a role in controlling the rate of propagation.

Fricker, HA, Young NW, Coleman R, Bassis JN, Minster JB.  2005.  Multi-year monitoring of rift propagation on the Amery Ice Shelf, East Antarctica. Geophysical Research Letters. 32   10.1029/2004gl021036   AbstractWebsite

We use satellite imagery from four sensors (Multi-angle Imaging SpectroRadiometer (MISR), Enhanced Thematic Mapper (ETM), and RADARSAT and ERS Synthetic Aperture Radar (SAR) to monitor the lengths of two rifts on the Amery Ice Shelf, from 1996 to 2004. We find that the rifts have each been propagating at a steady annual rate for the past 5 years. Superimposed on this steady rate is a seasonal signal, where propagation rates are significantly higher in the summer period (i.e., September-April) than in the winter period (i.e., April-September). Possible causes of this summer-winter effect are changing properties of the ice melange, which fills the rifts, and seasonal changes in ocean circulation beneath the ice shelf.

Fricker, HA, Bassis JN, Minster B, MacAyeal DR.  2005.  ICESat's new perspective on ice shelf rifts: The vertical dimension. Geophysical Research Letters. 32   10.1029/2005gl025070   AbstractWebsite

The small footprint (similar to 70 m) and similar to 172 m along-track spacing of the Geoscience Laser Altimeter System (GLAS) on the Ice, Cloud and land Elevation Satellite (ICESat) provides unprecedented horizontal resolution for a satellite altimeter. This enables ICESat to map many previously unresolved features on ice shelves, such as crevasses, rifts, grounding zones and ice fronts. We present examples of ICESat-derived elevation data showing topography over rifts on the Amery and Ross ice shelves, widths of rifts and as estimates of the thickness of melange (a collection of ice and snow trapped inside the rifts). We show that melange thickness remains constant over the ICESat data period and tends to be thicker in older rifts. We validate the ICESat-derived melange depth estimate with an in situ measurement on the Ross Ice Shelf.

2004
Heuze, F, Archuleta R, Bonilla F, Day S, Doroudian M, Elgamal A, Gonzales S, Hoehler M, Lai T, Lavallee D, Lawrence B, Liu PC, Martin A, Matesic L, Minster B, Mellors R, Oglesby D, Park S, Riemer M, Steidl J, Vernon F, Vucetic M, Wagoner J, Yang Z.  2004.  Estimating site-specific strong earthquake motions. Soil Dynamics and Earthquake Engineering. 24:199-223.   10.1016/j.soildyn.2003.11.002   AbstractWebsite

The Campus Earthquake Program (CEP) of the University of California (UC) started in March 1996, and involved a partnership among seven campuses of the UC-Berkeley, Davis, Los Angeles, Riverside, San Diego, Santa Barbara, Santa Cruz-and the Lawrence Livermore National Laboratory (LLNL). The aim of the CEP was to provide University campuses with site-specific assessments of their earthquake strong motion exposure, to complement estimates they obtain from consultants according to the state-of-the-practice (SOP), i.e. Building Codes (UBC 97, IBC 2000), and Probabilistic Seismic Hazard Analysis (PSHA). The Building Codes are highly simplified tools, while the more sophisticated PSHA is still somewhat generic in its approach because it usually draws from many earthquakes not necessarily related to the faults threatening the site under study. Between 1996 and 2001, the site-specific studies focused on three campuses: Riverside, San Diego, and Santa Barbara. Each campus selected 1-3 sites to demonstrate the methods and procedures used by the CEP: Rivera Library and Parking Lots (PL) 13 and 16 at UCR, Thornton Hospital, the Cancer Center, and PL 601 at UCSD, and Engineering I building at UCSB. The project provided an estimate of strong ground motions at each selected site, for selected earthquake scenarios. These estimates were obtained by using an integrated geological, seismological, geophysical, and geotechnical approach, that brings together the capabilities of campus and laboratory personnel. Most of the site-specific results are also applicable to risk evaluation of other sites on the respective campuses. The CEP studies have provided a critical assessment of whether existing campus seismic design bases are appropriate. Generally speaking, the current assumptions are not acknowledging the severity of the majority of expected motions. Eventually, both the results from the SOP and from the CEP should be analyzed, to arrive at decisions concerning the design-basis for buildings on UC campuses. Published by Elsevier Ltd.

2003
Calais, E, Haase JS, Minster JB.  2003.  Detection of ionospheric perturbations using a dense GPS array in Southern California. Geophysical Research Letters. 30   10.1029/2003gl017708   AbstractWebsite

[1] We present observations of high-frequency ionospheric perturbations detected using Global Positioning System (GPS) data from the Southern California Integrated GPS Network (SCIGN), a densely spaced GPS array of about 250 stations centered on the Los Angeles area. We show examples of perturbations with 3 - 10 minute periods that may result from coupling between the ionosphere and neutral gravity waves generated in the lower atmosphere. Although the signal-to-noise ratio of the perturbations is relatively small, we show how multi-station array processing techniques can take advantage of the high spatial density of the measurements and the coherence of the signal over a region the size of the SCIGN to considerably improve the detection capability.

2002
Fialko, Y, Sandwell D, Agnew D, Simons M, Shearer P, Minster B.  2002.  Deformation on nearby faults induced by the 1999 Hector Mine earthquake. Science. 297:1858-1862.   10.1126/science.1074671   AbstractWebsite

Interferometric Synthetic Aperture Radar observations of surface deformation due to the 1999 Hector Mine earthquake reveal motion on several nearby faults of the eastern California shear zone. We document both vertical and horizontal displacements of several millimeters to several centimeters across kilometer-wide zones centered on pre-existing faults. Portions of some faults experienced retrograde (that is, opposite to their long-term geologic slip) motion during or shortly after the earthquake. The observed deformation likely represents elastic response of compliant fault zones to the permanent co-seismic stress changes. The induced fault displacements imply decreases in the effective shear modulus within the kilometer-wide fault zones, indicating that the latter are mechanically distinct from the ambient crustal rocks.

Zwally, HJ, Schutz B, Abdalati W, Abshire J, Bentley C, Brenner A, Bufton J, Dezio J, Hancock D, Harding D, Herring T, Minster B, Quinn K, Palm S, Spinhirne J, Thomas R.  2002.  ICESat's laser measurements of polar ice, atmosphere, ocean, and land. Journal of Geodynamics. 34:405-445.   10.1016/s0264-3707(02)00042-x   AbstractWebsite

The Ice, Cloud and Land Elevation Satellite (ICESat) mission will measure changes in elevation of the Greenland and Antarctic ice sheets as part of NASA's Earth Observing System (EOS) of satellites. Time-series of elevation changes will enable determination of the present-day mass balance of the ice sheets, study of associations between observed ice changes and polar climate, and estimation of the present and future contributions of the ice sheets to global sea level rise. Other scientific objectives of ICESat include: global measurements of cloud heights and the vertical structure of clouds and aerosols; precise measurements of land topography and vegetation canopy heights; and measurements of sea ice roughness, sea ice thickness, ocean surface elevations, and surface reflectivity. The Geoscience Laser Altimeter System (GLAS) on ICESat has a 1064 nm laser channel for surface altimetry and dense cloud heights and a 532 nm lidar channel for the vertical distribution of clouds and aerosols. The predicted accuracy for the surface-elevation measurements is 15 em, averaged over 60 m diameter laser footprints spaced at 172 m alongtrack. The orbital altitude will be around 600 km at an inclination of 94degrees with a 183-day repeat pattern. The on-board GPS receiver will enable radial orbit determinations to better than 5 cm, and star-trackers will enable footprints to be located to 6 m horizontally. The spacecraft attitude will be controlled to point the laser beam to within 35 m of reference surface tracks at high latitudes. ICESat is designed to operate for 3-5 years and should be followed by successive missions to measure ice changes for at least 75 years. (C) 2002 Published by Elsevier Science Ltd.

Hudnut, KW, Borsa A, Glennie C, Minster JB.  2002.  High-resolution topography along surface rupture of the 16 October 1999 Hector Mine, California, earthquake (M-w 7. 1) from airborne laser swath mapping. Bulletin of the Seismological Society of America. 92:1570-1576.   10.1785/0120000934   AbstractWebsite

In order to document surface rupture associated with the Hector Mine earthquake, in particular, the area of maximum slip and the deformed surface of Lavic Lake playa, we acquired high-resolution data using relatively new topographic-mapping methods. We performed a raster-laser scan of the main surface breaks along the entire rupture zone, as well as along an unruptured portion of the Bullion fault. The image of the ground surface produced by this method is highly detailed, comparable to that obtained when geologists make particularly detailed site maps for geomorphic or paleoseismic studies. In this case, however, for the first time after a surface-rupturing earthquake, the detailed mapping is along the entire fault zone rather than being confined to selected sites. These data are geodetically referenced, using the Global Positioning System, thus enabling more accurate mapping of the rupture traces. In addition, digital photographs taken along the same fight lines can be overlaid onto the precise topographic data, improving terrain visualization. We demonstrate the potential of these techniques for measuring fault-slip vectors.