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K.W. Hudnut

Publications and source records attributed to K.W. Hudnut.

13 recordsLinked to original sources
USGS2012

Earthquake geodesy and hazard monitoring

Catastrophic events such as major earthquakes and volcanic eruptions result when the earth's crust fails in response to accumulated deformation. The accumulation of deformation results from ongoing processes such as aseismic deformation of subcrustal rock associated with relative plate motions, or the ascent of magma through a volcanic plumbing system. Geodetic measurements document the crustal deformation leading to these failures and the deformation resulting from them, providing unique insight into the physical processes involved. By virtue of the space and time domains of ground deformation detected with geodetic measurements, geodesy is a useful tool in monitoring active tectonic and volcanic regimes. For a wide range of natural events including earthquakes, aseismic fault motions, and volcanic events, geodetic measurements constrain physical models of the processes that cause such events. Because these geodetic studies probe the underlying processes leading to and culminating in catastrophic natural events, many such studies are directly applicable to earthquake and volcano hazard assessment.

California↗
USGS2010

Liquefaction caused by the 2009 Olancha, California (USA), M 5.2 earthquake

The October 3, 2009 (01:16:00 UTC), Olancha M 5.2 earthquake caused extensive liquefaction as well as permanent horizontal ground deformation within a 1.2 km 2 area earthquake in Owens Valley in eastern California (USA). Such liquefaction is rarely observed during earthquakes of M ≤ 5.2. We conclude that subsurface conditions, not unusual ground motion, were the primary factors contributing to the liquefaction. The liquefaction occurred in very liquefiable sands at shallow depth (< 2 m) in an area where the water table was near the land surface. Our investigation is relevant to both geotechnical engineering and geology. The standard engineering method for assessing liquefaction potential, the Seed–Idriss simplified procedure, successfully predicted the liquefaction despite the small earthquake magnitude. The field observations of liquefaction effects highlight a need for caution by earthquake geologists when inferring prehistoric earthquake magnitudes from paleoliquefaction features because small magnitude events may cause such features.

California↗
USGS2008

Broadband simulations for Mw 7.8 southern san andreas earthquakes: Ground motion sensitivity to rupture speed

Using the high-performance computing resources of the Southern California Earthquake Center, we simulate broadband (0-10 Hz) ground motions for three Mw 7.8 rupture scenarios of the southern San Andreas fault. The scenarios incorporate a kinematic rupture description with the average rupture speed along the large slip portions of the fault set at 0.96, 0.89, and 0.84 times the local shear wave velocity. Consistent with previous simulations, a southern hypocenter efficiently channels energy into the Los Angeles region along the string of basins south of the San Gabriel Mountains. However, we find the basin ground motion levels are quite sensitive to the prescribed rupture speed, with peak ground velocities at some sites varying by over a factor of two for variations in average rupture speed of about 15%. These results have important implications for estimating seismic hazards in Southern California and emphasize the need for improved understanding of earthquake rupture processes. Copyright 2008 by the American Geophysical Union.

Geophysical Research Letters↗
USGS2008

The wister mud pot lineament: Southeastward extension or abandoned strand of the San Andreas fault?

We present the results of a survey of mud pots in the Wister Unit of the Imperial Wildlife Area. Thirty-three mud pots, pot clusters, or related geothermal vents (hundreds of pots in all) were identified, and most were found to cluster along a northwest-trending line that is more or less coincident with the postulated Sand Hills fault. An extrapolation of the trace of the San Andreas fault southeastward from its accepted terminus north of Bombay Beach very nearly coincides with the mud pot lineament and may represent a surface manifestation of the San Andreas fault southeast of the Salton Sea. Additionally, a recent survey of vents near Mullet Island in the Salton Sea revealed eight areas along a northwest-striking line where gas was bubbling up through the water and in two cases hot mud and water were being violently ejected.

Bulletin of the Seismological Society of America↗
USGS2006

Uplift and subsidence associated with the great Aceh-Andaman earthquake of 2004

Rupture of the Sunda megathrust on 26 December 2004 produced broad regions of uplift and subsidence. We define the pivot line separating these regions as a first step in defining the lateral extent and the downdip limit of rupture during that great Mw ??? 9.2 earthquake. In the region of the Andaman and Nicobar islands we rely exclusively on the interpretation of satellite imagery and a tidal model. At the southern limit of the great rupture we rely principally on field measurements of emerged coral microatolls. Uplift extends from the middle of Simeulue Island, Sumatra, at ??? 2.5??N, to Preparis Island, Myanmar (Burma), at ??? 14.9??N. Thus the rupture is ??? 1600 km long. The distance from the pivot line to the trench varies appreciably. The northern and western Andaman Islands rose, whereas the southern and eastern portion of the islands subsided. The Nicobar Islands and the west coast of Aceh province, Sumatra, subsided. Tilt at the southern end of the rupture is steep; the distance from 1.5 m of uplift to the pivot line is just 60 km. Our method of using satellite imagery to recognize changes in elevation relative to sea surface height and of using a tidal model to place quantitative bounds on coseismic uplift or subsidence is a novel approach that can be adapted to other forms of remote sensing and can be applied to other subduction zones in tropical regions. Copyright 2006 by the American Geophysical Union.

Journal of Geophysical Research B: Solid Earth↗
USGS2006

Description of the L1C signal

Detailed design of the modernized LI civil signal (L1C) signal has been completed, and the resulting draft Interface Specification IS-GPS-800 was released in Spring 2006. The novel characteristics of the optimized L1C signal design provide advanced capabilities while offering to receiver designers considerable flexibility in how to use these capabilities. L1C provides a number of advanced features, including: 75% of power in a pilot component for enhanced signal tracking, advanced Weilbased spreading codes, an overlay code on the pilot that provides data message synchronization, support for improved reading of clock and ephemeris by combining message symbols across messages, advanced forward error control coding, and data symbol interleaving to combat fading. The resulting design offers receiver designers the opportunity to obtain unmatched performance in many ways. This paper describes the design of L1C. A summary of LIC's background and history is provided. The signal description then proceeds with the overall signal structure consisting of a pilot component and a carrier component. The new L1C spreading code family is described, along with the logic used for generating these spreading codes. Overlay codes on the pilot channel are also described, as is the logic used for generating the overlay codes. Spreading modulation characteristics are summarized. The data message structure is also presented, showing the format for providing time, ephemeris, and system data to users, along with features that enable receivers to perform code combining. Encoding of rapidly changing time bits is described, as are the Low Density Parity Check codes used for forward error control of slowly changing time bits, clock, ephemeris, and system data. The structure of the interleaver is also presented. A summary of L 1C's unique features and their benefits is provided, along with a discussion of the plan for L1C implementation.

Conference Paper↗
USGS2006

L1C signal design options

Design activities for a new civil signal centered at 1575.42 MHz, called L1C, began in 2003, and the Phase 1 effort was completed in 2004. The L1C signal design has evolved and matured during a Phase 2 design activity that began in 2005. Phase 2 has built on the initial design activity, guided by responses to international user surveys conducted during Phase 1. A common core of signal characteristics has been developed to provide advances in robustness and performance. The Phase 2 activity produced five design options, all drawing upon the core signal characteristics, while representing different blends of characteristics and capabilities. A second round of international user surveys was completed to solicit advice concerning these design options. This paper provides an update of the L1C design process, and describes the current L1C design options. Initial performance estimates are presented for each design option, displaying trades between signal tracking robustness, the speed and robustness of clock and ephemeris data, and the rate and robustness of other data message contents. Planned remaining activities are summarized, leading to optimization of the L1C design.

Conference Paper↗
USGS2004

Slip history of the 2003 San Simeon earthquake constrained by combining 1-Hz GPS, strong motion, and teleseismic data

The slip history of the 2003 San Simeon earthquake is constrained by combining strong motion and teleseismic data, along with GPS static offsets and 1-Hz GPS observations. Comparisons of a 1-Hz GPS time series and a co-located strong motion data are in very good agreement, demonstrating a new application of GPS. The inversion results for this event indicate that the rupture initiated at a depth of 8.5 km and propagated southeastwards with a speed ???3.0 km/sec, with rake vectors forming a fan structure around the hypocenter. We obtained a peak slip of 2.8 m and total seismic moment of 6.2 ?? 1018 Nm. We interpret the slip distribution as indicating that the hanging wall rotates relative to the footwall around the hypocenter, in a sense that appears consistent with the shape of the mapped fault trace. Copyright 2004 by the American Geophysical Union.

Geophysical Research Letters↗
USGS2004

Dynamic rupture modeling of the transition from thrust to strike-slip motion in the 2002 Denali fault earthquake, Alaska

We use three-dimensional dynamic (spontaneous) rupture models to investigate the nearly simultaneous ruptures of the Susitna Glacier thrust fault and the Denali strike-slip fault. With the 1957 Mw 8.3 Gobi-Altay, Mongolia, earthquake as the only other well-documented case of significant, nearly simultaneous rupture of both thrust and strike-slip faults, this feature of the 2002 Denali fault earthquake provides a unique opportunity to investigate the mechanisms responsible for development of these large, complex events. We find that the geometry of the faults and the orientation of the regional stress field caused slip on the Susitna Glacier fault to load the Denali fault. Several different stress orientations with oblique right-lateral motion on the Susitna Glacier fault replicate the triggering of rupture on the Denali fault about 10 sec after the rupture nucleates on the Susitna Glacier fault. However, generating slip directions compatible with measured surface offsets and kinematic source inversions requires perturbing the stress orientation from that determined with focal mechanisms of regional events. Adjusting the vertical component of the principal stress tensor for the regional stress field so that it is more consistent with a mixture of strike-slip and reverse faulting significantly improves the fit of the slip-rake angles to the data. Rotating the maximum horizontal compressive stress direction westward appears to improve the fit even further.

Alaska↗
USGS1998

Detection of aquifer system compaction and land subsidence using interferometric synthetic aperture radar, Antelope Valley, Mojave Desert, California

Interferometric synthetic aperture radar (InSAR) has great potential to detect and quantify land subsidence caused by aquifer system compaction. InSAR maps with high spatial detail and resolution of range displacement (±10 mm in change of land surface elevation) were developed for a groundwater basin (∼10 3 km 2 ) in Antelope Valley, California, using radar data collected from the ERS-1 satellite. These data allow comprehensive comparison between recent (1993–1995) subsidence patterns and those detected historically (1926–1992) by more traditional methods. The changed subsidence patterns are generally compatible with recent shifts in land and water use. The InSAR-detected patterns are generally consistent with predictions based on a coupled model of groundwater flow and aquifer system compaction. The minor inconsistencies may reflect our imperfect knowledge of the distribution and properties of compressible sediments. When used in conjunction with coincident measurements of groundwater levels and other geologic information, InSAR data may be useful for constraining parameter estimates in simulations of aquifer system compaction.

California↗
USGS1993

Detection of crustal deformation from the Landers earthquake sequence using continuous geodetic measurements

The measurement of crustal motions in technically active regions is being performed increasingly by the satellite-based Global Positioning System (GPS) 1,2 , which offers considerable advantages over conventional geodetic techniques 3,4 . Continuously operating GPS arrays with ground-based receivers spaced tens of kilometres apart have been established in central Japan 5,6 and southern California to monitor the spatial and temporal details of crustal deformation. Here we report the first measurements for a major earthquake by a continuously operating GPS network, the Permanent GPS Geodetic Array (PGGA) 7–9 in southern California. The Landers (magnitude Afw of 7.3) and Big Bear ( M w 6.2) earthquakes of 28 June 1992 were monitored by daily observations. Ten weeks of measurements, centred on the earthquake events, indicate significant coseismic motion at all PGGA sites, significant post-seismic motion at one site for two weeks after the earthquakes, and no significant preseismic motion. These measurements demonstrate the potential of GPS monitoring for precise detection of precursory and aftershock seismic deformation in the near and far field.

Nature↗