G13B-1222
An EarthScope Plate Boundary Observatory Progress Report
UNAVCO is building and operating the Plate Boundary Observatory (PBO), part of the NSF-funded EarthScope project to understand the structure, dynamics, and evolution of the North American continent. When complete in October 2008, the 875 GPS, 103 strain and seismic, and 28 tiltmeters stations will comprise the largest integrated geodetic and seismic network in United States and the second largest in the world. Data from the PBO network will facilitate research into plate boundary deformation with unprecedented scope and detail. As of 1 September 2007, UNAVCO had completed 680 PBO GPS stations and had upgraded 89% of the planned PBO Nucleus stations. Highlights of the past year's work include the expansion of the Alaska subnetwork to 95 continuously-operating stations, including coverage of Akutan and Augustine volcanoes and reconnaissance for future installations on Unimak Island; the installation of nine new stations on Mt. St. Helens; and the arrival of 33 permits for station installations on BLM land in Nevada. The Augustine network provided critical data on magmatic and volcanic processes associated with the 2005-2006 volcanic crisis, and has expanded to a total of 11 stations. Please visit http://pboweb.unavco.org/?pageid=3 for further information on PBO GPS network construction activities. As of September 2007, 41 PBO borehole stations had been installed and three laser strainmeter stations were operating, with a total of 60 borehole stations and 4 laser strainmeters expected by October 2007. In response to direction from the EarthScope community, UNAVCO installed a dense network of six stations along the San Jacinto Fault near Anza, California; installed three of four planned borehole strainmeter stations on Mt. St. Helens; and has densified coverage of the Parkfield area. Please visit http://pboweb.unavco.org/?pageid=8 for more information on PBO strainmeter network construction progress. The combined PBO/Nucleus GPS network provides 350 GB of raw standard rate data, with special downloads of more than 250 GB of high-rate GPS data following large earthquakes in Russia, Tonga, and Peru, as well as for community requests. The standard rate GPS data are processed routinely to generate data products including station position time series, velocity vectors, and related information, and all data products are available from the UNAVCO Facility archive. The PBO seismic network seismic network has provided 201 GB of raw data, which are available via Antelope and Earthworm from PBO and via the IRIS Data Management Center (DMC); we provide data to seismic networks operated from Caltech, UCSD, UCSB, University of Washington, and the Pacific Geosciences Center in Sidney, BC. The PBO strainmeter network has provided 93 GB of raw data, available in both raw native format and SEED format from the Northern California Earthquake Data Center and the IRIS DMC, along with higher-level products such as cleaned strain time series and related information. Please visit http://pboweb.unavco.org/gps_data and http://pboweb.unavco.org/strain_data for more information on PBO GPS and strainmeter/seismic data products, respectively. http://pboweb.unavco.org/
G13B-1223
Integration of the Plate Boundary Observatory and Existing GPS Networks in Southern California: A Multi Use Geodetic Network
The ultra-stable GPS monument design developed by Southern California Geodetic Network (SCIGN) in the late 1990s demonstrates sub-millimeter errors on long time series where there are a high percentage of observations and low multipath. Following SCIGN, other networks such as PANGA and BARGEN have adopted the monument design for both deep drilled braced monuments (DDBM = 5 legs grouted 10.7 meters into bedrock/stratigraphy) and short drilled braced monuments (SDBM = 4 legs epoxied 2 meters into bedrock). A Plate Boundary Observatory (PBO) GPS station consists of a "SCIGN" style monument and state of the art NetRS receiver and IP based communications. Between the years 2003-2008 875 permanent PBO GPS stations are being built throughout the United States. Concomitant with construction of the PBO the majority of pre-existing GPS stations that meet stability specifications are being upgraded with Trimble NetRS and IP based communications to PBO standards under the EarthScope PBO Nucleus project. In 2008, with completed construction of the Plate Boundary Observatory, more than 1100 GPS stations will share common design specifications and have identical receivers with common communications making it the most homogenous geodetic network in the World. Of the 875 total Plate Boundary Observatory GPS stations, 211 proposed sites are distributed throughout the Southern California region. As of August 2007 the production status is: 174 stations built (81 short braced monuments, 93 deep drilled braced monuments), 181 permits signed, 211 permits submitted and 211 station reconnaissance reports. The balance of 37 stations (19 SDBM and 18 DDBM) will be built over the next year from Long Valley to the Mexico border in order of priority as recommended by the PBO Transform, Extension and Magmatic working groups. Fifteen second data is archived for each station and 1 Hz as well as 5 Hz data is buffered to be triggered for download in the event of an earthquake. Communications equipment includes CDMA Proxicast modems, Hughes Vsat, Intuicom 900 MHz Ethernet bridge radios and several "real-time" sites use 2.4 GHz Wilan radios. Ultimately, 125 of the existing former-SCIGN GPS stations will be integrated into the So Cal region of PBO, of which 25 have real-time data streams. At the time of this publication the total combined Southern California region has over 40 stations streaming real-time data using both radios and CDMA modems. The real-time GPS sites provide specific benefits beyond the standard GPS station: they can provide a live correction for local surveyors and can be used to trigger an alarm if large displacements are recorded. The cross fault spatial distribution of these 336 GPS stations in the seismically active southern California region has the grand potential of augmenting a strong motion earthquake early warning system.
G13B-1224
Logistical Support for the Installation of the Plate Boundary Observatory GPS and Borehole Strainmeter Networks
The Plate Boundary Observatory (PBO), part of the NSF-funded EarthScope project, is designed to study the three- dimensional strain field resulting from deformation across the active boundary zone between the Pacific and North American plates in the western United States. To meet these goals, UNAVCO will install 880 continuous GPS stations, 103 borehole strainmeter stations, 28 tiltmeters, and five laser strainmeters by October 2008. Such a broad network presents significant logisitical challenges, including moving supplies, equipment, and personnel around 6 million square kilometers, and this requires accurate tracking and careful planning. The PBO logistics chain includes the PBO headquarters at UNAVCO in Boulder, Colorado and five regional offices in the continental United States and Alaska, served by dozens of suppliers spread across the globe. These offices are responsible for building and maintaining sites in their region. Most equipment and supplies first arrive in Boulder, where they are tagged and entered into a UNAVCO-wide equipment database, assembled and quality checked as necessary, and sent on to the appropriate regional office. Larger items which are costly to store and ship from Boulder, such as batteries or long sections of stainless steel pipe and bar required for monuments, are shipped directly from the supplier to each region as needed. These supplies and equipment are also tracked through the ordering, delivery, installation, and maintenance cycle via Earned Value Management techniques which allow us to meet NSF and other Federal procurement rules. Early prototypes and assembly configurations aid the development of material and supply budgets. A thorough understanding of Federal procurement rules at project start up is critical as the project moves forward.
G13B-1225
The RING and Seismic Network: Data Acquisition of Co-located Stations
The plate boundary between Africa and Eurasia represents an interesting geodynamical region characterized by a complex pattern of deformation. First-order scientific problems regarding the existence of rigid blocks within the plate boundary, the present-day activity of the Calabrian subduction zone and the modes of release of seismic deformation are still awaiting for a better understanding. To address these issues, the INGV (Istituto Nazionale Geofisica e Vulcanlogia) deployed a permanent, integrated and real-time monitoring GPS network (RING) all over Italy. RING is now constituted by about 120 stations. The CGPS sites, acquiring at 1Hz and 30s sampling rate, are integrated either with broad band or very broad band seismometers and accelerometers for an improved definition of the seismically active regions. Most of the sites are connected to the acquisition centre (located in Rome and duplicated in Grottaminarda) through a satellite system (VSAT), while the remaining sites transmit data by Internet and classical phone connections. The satellite data transmission and the integration with seismic instruments makes this network one of the most innovative CGPS networks in Europe. The heterogeneity of the installed instrumentation, the transmission types and the increasing number of stations needed a central monitoring and acquisition system. A central acquisition system has been developed in Grottaminarda in southern Italy. Regarding the seismic monitoring we chose to use the open source system Earthworm, developed by USGS, with which we store waveforms and implement automatic localization of the seismic events occurring in the area. As most of the GPS sites are acquired by means of Nanometrics satellite technology, we developed a specific software (GpsView), written in Java, to monitor the state of health of those CGPS. This software receives GPS data from NaqsServer (Nanometrics acquisition system) and outputs information about the sites (i.e. approx position, number of satellites) in real-time. Furthermore also a web-based application for the management of the data and the metadata relative to the GPS sites of the RING has been developed. We present (a) the existing and planned CGPS site distribution, (b) the technological description of the seismic and GPS data acquisitions in Grottaminarda INGV centre, and (c) the first results of CGPS data analysis.
G13B-1226
FOSFORE: project for distributions of French seismological data
FOSFORE (Fédération de l'Observation Sismologique Française) is a collaborative inter-university project aimed to distribute data of French permanent and temporary seismic networks and to make them freely available for the scientific community. FOSFORE is designed as a distributed data archive and is organized around four data centers located in universities at Grenoble, Nice, Paris, and Strasbourg. Currently available data include records of the GEOSCOPE global seismic network (Paris data center), of the French broadband seismic network (Nice and Strasbourg data centers), of the French accelerometric permanent network RAP (Grenoble data center), of numerous French temporary seismic deployments from different regions in the World (Grenoble data center), of the Corinth Rift Laboratory (Grenoble data center), and of regional monitoring networks in France. Waveform data are made freely available for download via NetDC and AutoDRM data request systems and Web interfaces. In the near future, we plan to incorporate more temporary deployments as well as data from volcano-monitoring networks in La Reunion Island and French Antilles and data from the North Chile seismic experiment. In addition, we are developing a centralized Web portal to access French seismological data, by connecting data centers via standard data request protocols such as NetDC and WebDC/Arclink. This facility will allow a better integration of the French data into the international data exchange system.
G13B-1227
Challenges of the GEOSCOPE Observatory.
The GEOSCOPE observatory consists of a global seismic network and a data center. The observatory was launched in 1982 by the French National Center of Scientific Research (CNRS/INSU) and progressively 30 stations have been installed across all continents and on islands throughout the oceans. The GEOSCOPE stations are located on 18 countries and equipped with three component very broad-band seismometers (STS1 or STS2) and 24 or 26 bit digitizers, as required by the Federation of Seismic Digital Network (FDSN). In most stations a pressure gauge and a thermometer are also installed. During the last years, 13 stations have been upgraded in order to send data in real or near real time to GEOSCOPE Data Center. In 2008, two new real time stations will be installed in the Indian Ocean: in the South of Madagascar and on Rodrigues island. Four stations in the Carribean region and in South America will also be upgraded to send real time data to GEOSCOPE Data Center and to local tsunami warning centers. Continuous data of all stations are collected in real time or with a delay by the GEOSCOPE Data Center in Paris where they are validated, stored and made accessible to the international scientific community. Users have free and open access to: - real time data from 13 stations. These data are transfered from the stations to the Geoscope Data Center using the seedlink protocol developed by GEOFON. Seedlink also enables to make these data accessible to the Tsunami Warning Centers and to other data center. These data are available to users through the GEOSCOPE web interface. - validated continous waveforms and meta data of all stations by using the NetDC system (Networked Data Centers). Data can be requested from the GEOSCOPE Data Center and from other networked centers associated to the FDSN. - a selection of seismograms corresponding to large earthquakes via a web interface - the power spectrum estimates of the seismic noise averaged over sequences of 24 hours for each station. The noise levels of the past 10 years of continuous data has been computed and are accessible via the web. The noise level of real time data is computed at day-8. GEOSCOPE data center is now networked to the French virtual data center, FOSFORE, in order to give a unique access to french seismological data. In Europe, GEOSCOPE data center participates in NERIES project (NA3 activity) in order to create a distributed archive and database for all continuous digital waveform recordings of the Euro-Mediterranean region.
G13B-1228
A High-Rate Continuous GPS Network in Iceland for Crustal Deformation Research
A significant expansion of the current continuous GPS network in Iceland is well underway. The goal of the project is to install 30-40 new continuous GPS stations, with a sampling rate of 1 second or higher in selected areas of the country. Most of the sites are already installed and are collecting data and communications are being established. Currently we have in total about 50 continuous and 12 semi-continuous stations running. Eventually, the older continuous GPS stations (installed from 1999 onwards) will also be upgraded to allow high sampling rates. Many of the CGPS sites are co-located with stations in the national seismic network which is very beneficial for operation of the sites and enhanced monotoring capabilities. The national seismic network in Iceland contains 51 3-component digital stations that all are on-line. High-rate GPS observations have been used successfully to study dynamic earthquake rupture processes, for example the Denali earthquake in Alaska and the 2003 Tokachi-Oki earthquake in Japan. New GPS stations were installed in seismically active areas in the South Iceland Seismic Zone, the Reykjanes Peninsula and in Northern Iceland. We also attempt to capture volcanic processes by installing high-rate GPS stations near the three most active volcanoes in Iceland: Hekla, Grímsvotn, and Katla. These volcanoes have been active recently or are currently showing signs of unrest. Continuous GPS and recent campaign GPS measurements indicate rapid uplift (up to 2 cm/yr) over a wide area in central Iceland due to retreat of the glaciers in a warming climate. The new network already installed in central Iceland will obtain more detailed information on the rate and extent of the uplift. Implementing the 1-Hz technology in Iceland enables studies of both the dynamic as well as slower-rate processes related to earthquake and volcanic activity. The high level of volcanic and earthquake activity in Iceland makes it an ideal site for this project. In addition, we have nearly tripled the number of continuous GPS stations in Iceland, improving constraints on the plate spreading in Iceland, as well as increasing our understanding of volcanic and tectonic interaction. http://www.norvol.hi.is/~thora/ondvegi.html
G13B-1229
EarthScope Website Revised
EarthScope is an ambitious, multidisciplinary program funded by the National Science Foundation to explore the structure and evolution of the North American continent and understand processes controlling earthquakes and volcanoes. The EarthScope program web site (http://www.earthscope.org) gives an initial introduction to the purpose, scope, and benefits of one of the largest NSF-funded programs ever undertaken. It also acts as the central point of information dissemination for the scientific community and a resource repository for education and outreach purposes. Over the past year, the EarthScope program Web site has been redesigned to simplify access to information while developing a larger focus on the scientific perspective derived from this uniquely inter-disciplinary program. A new categorical orientation of the EarthScope program observatories, instruments, and data availability provides new visitors a more cohesive understanding of the component facility role and a clear introduction to the organizations responsible for each facility. Though the EarthScope program web site primarily provides introductory level information and announcements, new and intuitive features are being implemented routinely. A Beta release of the new EarthScope Google Map allows a broader audience to view and access instrument station information in a way that is familiar and informative. Centralized links to visualizations and other multi-media products that showcase scientific interpretations derived from EarthScope instrument data provides a greater comprehension of the scope and benefits of this program. http://www.earthscope.org
G13B-1230
Data Access and Web Services at the EarthScope Plate Boundary Observatory
The EarthScope Plate Boundary Observatory (PBO) at UNAVCO, Inc., part of the NSF-funded EarthScope project, is designed to study the three-dimensional strain field resulting from deformation across the active boundary zone between the Pacific and North American plates in the western United States. To meet these goals, PBO will install 880 continuous GPS stations, 103 borehole strainmeter stations, and five laser strainmeters, as well as manage data for 209 previously existing continuous GPS stations and one previously existing laser strainmeter. UNAVCO provides access to data products from these stations, as well as general information about the PBO project, via the PBO web site (http://pboweb.unavco.org). GPS and strainmeter data products can be found using a variety of access methods, incuding map searches, text searches, and station specific data retrieval. In addition, the PBO construction status is available via multiple mapping interfaces, including custom web based map widgets and Google Earth. Additional construction details can be accessed from PBO operational pages and station specific home pages. The current state of health for the PBO network is available with the statistical snap-shot, full map interfaces, tabular web based reports, and automatic data mining and alerts. UNAVCO is currently working to enhance the community access to this information by developing a web service framework for the discovery of data products, interfacing with operational engineers, and exposing data services to third party participants. In addition, UNAVCO, through the PBO project, provides advanced data management and monitoring systems for use by the community in operating geodetic networks in the United States and beyond. We will demonstrate these systems during the AGU meeting, and we welcome inquiries from the community at any time. http://pboweb.unavco.org
G13B-1231
GPS data exploration for seismologists and geodesists
Over the past decade, GPS and seismic networks spanning the western US plate boundaries have produced vast amounts of data that need to be made accessible to both the geodesy and seismology communities. Unlike seismic data, raw geodetic data requires significant processing before geophysical interpretations can be made. This requires the generation of data-products (time series, velocities and strain maps) and dissemination strategies to bridge these differences and assure efficient use of data across traditionally separate communities. "GPS DATA PRODUCTS FOR SOLID EARTH SCIENCE" (GDPSES) is a multi-year NASA funded project, designed to produce and deliver high quality GPS time series, velocities, and strain fields, derived from multiple GPS networks along the western US plate boundary, and to make these products easily accessible to geophysicists. Our GPS product dissemination is through modern web-based IT methodology. Product browsing is facilitated through a web tool known as GPS Explorer and continuous streams of GPS time series are provided using web services to the seismic archive, where it can be accessed by seismologists using traditional seismic data viewing and manipulation tools. GPS-Explorer enables users to efficiently browse several layers of data products from raw data through time series, velocities and strain by providing the user with a web interface, which seamlessly interacts with a continuously updated database of these data products through the use of web-services. The current archive contains GDPSES data products beginning in 1995, and includes observations from GPS stations in EarthScope's Plate Boundary Observatory (PBO), as well as from real-time real-time CGPS stations. The generic, standards-based approach used in this project enables GDPSES to seamlessly expand indefinitely to include other space-time-dependent data products from additional GPS networks. The prototype GPS-Explorer provides users with a personalized working environment in which the user may zoom in and access subsets of the data via web services. It provides users with a variety of interactive web tools interconnected in a portlet environment to explore and save datasets of interest to return to at a later date. At the same time the GPS time series are also made available through the seismic data archive, where the GPS networks are treated as regular seismic networks, whose data is made available in data formats used by seismic utilities such as SEED readers and SAC. A key challenge, stemming from the fundamental differences between seismic and geodetic time series, is the representation of reprocessed of GPS data in the seismic archive. As GPS processing algorithms evolve and their accuracy increases, a periodic complete recreation of the the GPS time series archive is necessary.
G13B-1232
AUV-aided Seafloor Geodetic Observation System
We launched a project supported by the Japan Society for the Science Promotion as the Grants in Aid for Scientific Research. In this project, we are aiming at developing new-generation seafloor geodetic observation system that conquers difficulties inherent with the current system. Central idea of this project is to utilize techniques of underwater robot (Autonomous Underwater Vehicle) and seafloor platform to make measurements in place of using the research vessels. Combination of underwater robot and seafloor platform make it possible to conduct the observation with selecting favorable condition of sea and GPS satellite distributions, to make much more frequent observations and to enable flexible planning of observation in response to sudden geodetic events. Trial model of the on-board and the seafloor units were finished. Space-saving design for the on-board unit, which controls both acoustic ranging system and GPS, was one of big issues to be overcome. We reviewed the current system configuration and made it simple. It was miniaturized, and then it was put into two cylinders. The cylinder No.1 contains the PHINS (IXSEA), an inertial navigation system based on fiber optic gyroscope technology. Another one, the cylinder No.2, contains the SF-2050M (NAVCOM Technology) GPS receiver and the acoustic ranging units. The original chassis of the SF-2050M was removed to minimize the volume of the unit and then only the electrical boards of the GPS receiver was installed into the cylinder No.2. There is no commercialized GPS antenna that can receive both L1 and L2 signals and has pressure capability of 2,000 m depth in the sea. Then we developed the pressure housing for the GPS antenna. The small size antenna corresponding to the L1 and L2 signals was installed in it. The transducer, for underwater acoustic ranging, employed on both the on-board and the seafloor units has been newly developed by Dr. Tom Ensign, Engineering acoustic Inc.. This transducer has a spherical ceramic oscillator so that it has an omni directional feature in acoustic phase response. We have performed evaluation tests for the new system. Two of them were done with AUVs in the Sagami Bay. The AUV that we utilized was one named gr2D4h. The r2D4 is an intelligent AUV developed by Prof. Tamaki Ura, the Underwater Technology Research Center, IIS. The others have been conducted with the mock-up of AUV. The on-board unit was installed on the mock-up, and the mock-up was towed by small boat during acoustic ranging. We will report the overview of the AUV-aided geodetic observation system and its performance, based on the several performance evaluation tests that were already done and will be done.
G13B-1233
Development of the seafloor acoustic ranging system
We have developed a seafloor acoustic ranging system, which simulates an operation with the DONET (Development of Dense Ocean-floor Network System for Earthquake and Tsunami) cable, to monitor seafloor crustal movement. The seafloor acoustic ranging system was based on the precise acoustic transponder (PXP). We have a few problems for the improvement of the resolution. One thing is the variation of sound speed. Another is the bending of ray path. A PXP measures horizontal distances on the seafloor from the round trip travel times of acoustic pulses between pairs of PXP. The PXP was equipped with the pressure, temperature gauge and tilt-meter. The variation of sound speed in seawater has a direct effect on the measurement. Therefore we collect the data of temperature and pressure. But we donft collect the data of salinity because of less influence than temperature and pressure. Accordingly a ray path of acoustic wave tends to be bent upward in the deep sea due to the Snellfs law. As the acoustic transducer of each PXPs held about 3.0m above the seafloor, the baseline is too long for altitude from the seafloor. In this year we carried out the experiment for the seafloor acoustic ranging system. We deployed two PXPs at about 750m spacing on Kumano-nada. The water depth is about 2050m. We collected the 660 data in this experiment during one day. The round trip travel time show the variation with peak-to-peak amplitude of about 0.03msec. It was confirmed to explain the majority in this change by the change in sound speed according to the temperature and pressure. This results shows the resolution of acoustic measurements is +/-2mm. Acknowledgement This study is supported by gDONETh of Ministry of Education, Culture, Sports, Science and Technology.
G13B-1234
Monitoring the Lateral Gradient of Sound Speed in Ocean Toward Fast GPS/Acoustic Seafloor Positioning for the Cabled System
The GPS/acoustic technique is now in practical use for seafloor positioning to monitor crustal deformation beneath the ocean, where land-based GPS networks are not available. To achieve semi-realtime monitoring of the strain accumulation and possible precursor for the expected Nankai earthquake in Japan, JAMSTEC and others have started so called DONET project (Development of Dense Ocean-floor Network System for Earthquakes and Tsunamis), funded by MEXT Japan, where numerous seismometers, pressure gauges, and acoustic ranging instruments are going to be equipped through the planing seafloor cables at Kumano-nada. A GPS/acoustic system will be combined in part of the cable system. The present GPS/acoustic survey, which acoustically measures slant ranges between a surface transducer and three seafloor transponders, has a fault to get position in semi-realtime. The problem setting supposes a laterally stratified sound speed structure. Violation of this condition with lateral gradient in sound speed results in the deviation of apparent position of the transponders. At present, ~5~cm of accuracy is achieved after taking time-average more than 1~day to cancel-out the time-varying direction of the gradient. In addition, if a long-lived gradient appeared, we have no way to distinguish seafloor displacement from the gradient. To overcome the present status, we propose a new survey style which actively estimates the sound speed gradient and makes its correction on apparent positioning by using five transponders. This rather complicated survey style requires severe layout of the transponders and observing position to stably resolve five unknowns: the horizontal displacement vector, stratified sound speed, and its gradient vector. We numerically investigated the best arrangement by evaluating the condition number of the observation equations. For further application, we also diagnosed the case of the reduced number of the unknowns and transponders for lower-cost construction of a seafloor station, such that direction of the displacement is known or expected in advance based on other geophysical or geological informations. http://www.aob.geophys.tohoku.ac.jp/dmg/gpsa/
G13B-1235
High-Rate GPS Data - When are They Useful?
High-rate GPS signals have recently been shown to clearly record measurable displacements at long periods from teleseismic and regional distances from large earthquakes (e.g. 2002 Mw7.9 Denali and 2003 Mw8.3 Tokachi-Oki) and at shorter periods from moderate earthquakes (2003 Mw6.5 San Simeon and 2004 Mw6.0 Parkfield). The ability to directly record broadband displacement - including static offsets - without sensitivity to tilting and without the risk of clipping, means high-rate GPS data are an ideal compliment to existing strong motion networks for recording near-source and regional ground motions. This is especially the case near subduction zone regions where major events with significant displacements and rotations over a wide area are expected. Current high-rate GPS processing provides accuracy of 5-10 mm (depending on the component) at periods less than 5 minutes. It is not clear what limitation this minimum signal resolution should have on the deployment of future high-rate GPS stations and archival of the high-rate data. Should high-rate GPS capability be included within GPS networks only near major faults, and should the high-rate data be continuously archived and processed, or only triggered during large events? This study looks at event and noise signals from 1sps GPS stations which recorded the Parkfield, Denali, San Simeon, and Tokachi-Oki events. We provide an estimation of the background noise across a broad frequency spectrum, from 0.5Hz to 1000s. We compare the GPS noise estimates with previous seismic studies of noise and event signals in terms of acceleration, velocity and displacement.
G13B-1236
GPS Seismology Results from the 2002 M=7.9 Denali Fault Earthquake
In order to properly combine traditional seismic measurements with high-rate (1-Hz) GPS positions, we must first understand the relative strengths of each data type and the inherent precision and accuracy of high-rate GPS positions. Here, we characterize the strengths and limitations of GPS seismology with a case study of the Mw=7.9 Denali Fault earthquake of 2002, utilizing high-rate GPS data from 23 stations across much of western North America to epicentral distances of about 3500 km. First, after applying error reduction methods to GPS displacements, we estimate noise floors of 4-10 mm in the horizontal, and 10-20 mm in the vertical for these stations and this event. Next, we access the accuracy of these GPS positions by comparing four collocated GPS and broadband seismometer recordings in western Canada. By integrating the seismic data to displacement and applying common filters to the seismic and GPS data, we find that the high-rate GPS and broadband seismic data are in excellent agreement for the 10-50 second period surface waves of the Denali earthquake as long as the amplitudes exceed about 1 cm. Finally, given this validation of the GPS displacements for this event, the complete "GPS seismogram" dataset for the 23 stations is now archived at IRIS and available for public use in future studies of the 2002 Denali fault earthquake. Integrating seismic and GPS data provides much larger data sets for studies of the earthquake source (including mechanism and directivity) and wave propagation effects.
G13B-1237
Seismic Ground Motion and Coseismic Displacement Associated with the 26 December 2006 off Pingtung, Taiwan, Earthquake
Two sequence earthquakes (ML=6.96 and 6.99) occurred in southern Taiwan off Pingtung, and the main shocks are only at an interval of 8 minutes. These earthquakes caused more than ten centimeters of ground motion, and a few centimeters of coseismic deformation, respectively. All of these displacements have been recorded by the Continuously Observation Recording GPS Stations (CORS), and estimated by two different post-processing methods, namely the kinematic positioning and the daily solution algorithm. Precise evaluation of the capturing instantaneous ground motion and coseismic deformation at a level of just millimeters requires rigorous computational procedures. In this paper, a set of high sampling rate (1Hz) data from the CORS has been used to study simultaneous ground motion during the Pingtung earthquakes. A completely regular algorithm to estimate the crustal deformation in the Taiwan area has been applied to acquire coseismic deformation as a result of the Pingtung earthquakes. Applying beyond 2 weeks of data and 50 stations of the CORS, the coseismic deformation can be precisely estimated. Since the instantaneous ground motion can be computed by continuous GPS observations and the coseismic deformation can be acquired precisely and integrated with seismic data, these results can assist the study of earthquake geodesy.
G13B-1238
Observation and modeling of thermoelastic strain in Parkfield borehole strainmeter records
Strainmeters installed in deep (> 150m) boreholes in the Parkfield region show pronounced seasonal fluctuations, including a strong annual component. We suggest that a significant part of the annual variations in these strain records is caused by strain in the elastic part of the earth's crust induced by variations in atmospheric temperature at the surface. We test this hypothesis by computing the thermoelastic strain from the atmospheric temperature record observed at the weather station at Coalinga, and compare it to the strain recorded by dilatometers installed in boreholes near Parkfield. We use a thermoelastic strain model which computes the thermoelastic strain for an elastic half space with a decoupled unconsolidated (soil or gravel) upper layer. The source of the strain in the elastic solid is a spatially varying temperature field that travels through the unconsolidated surface layer, and whose local horizontal length scale is related to topography and lateral material heterogeneities. The strain in the underlying half-space, generated by temperature variations at the base of the decoupled surface layer, is calculated with an analytical solution for thermoelastic strain in a homogeneous half-space. Our simple model provides a good first-order fit to the annual signals recorded at the borehole-installed strainmeters, including one located as deep as 320 m. The two parameters yielded by the model, the thickness of the unconsolidated upper layer (~1 meter) and the wavelength of the source field (2.75 km) are sufficiently plausible to support the physical validity of the thermoelastic strain model. Removal of the thermoelastic strain signal from strainmeter records would provide better understanding of the remaining noise sources and allow clearer focus on tectonic signals.
G13B-1239
Landslide monitoring using multi-antenna GPS deformation monitoring system
GPS has already widely applied in civil engineering, fault detecting and landslide monitoring in the last decade, because of its convenience and high precision. However, GPS receiver is very expensive. If we want to monitor the landslide twenty-four hours a day, we need to buy a lot of GPS receivers. In order to spend less cost, multi- antenna GPS deformation monitoring system was employed to monitor the landslide of the freeway at Guansi section in Taiwan. Moreover, the data from 3D laser scanner, rain gauge, inclinometer and water table meter were utilized to analysis the movement of this landslide to make sure the safety of the drivers.
G13B-1240
ERROR ANALYSIS OF STRAIN RATES FROM GPS MEASUREMENTS
At first, we calculate the strain rates from GPS vectors with the approach combining kriging method with the derivative of shape functions. Then we propose a method to carry out error analysis of the strain rates, estimated from GPS vectors with measurement errors, on the base of Monte Carlo technique. The result shows that the orientations of principal strain rates are consistent with those of the P axis and T axis of focal mechanisms. The absolute value of the component of strain rate in the west of China is approximately 5 times larger than that of eastern China on the whole. Taken the Chinese continent as an example, independent computation of strain rates is repeated for a large number of times, and the errors as well as the components of strain rates, are computed through statistical theory. The error result shows that the errors of principal strain rates are larger in Himalayas and in the east side of the Tibetan plateau than those in other places. However, the relative errors in the East China are much larger than those in the west China such as in and around the region of the Tibet. In general, the strain rates in the west China are accurate and stable. The strain rate and its error results reveal that the orientations of principal strain rates are consistent with those of tectonic stresses in and around the Tibet. And especially the tensile strain rates from GPS vector data in the interior and in the southeast of the Tibet are in good agreement with the seismic and geological observations.