G43A-01
A study of risk in the metropolitan area of Guadalajara through dense GPS geodesy
Geodesic measurements from the Global Positioning System (GPS) are used extensively for basic earth science research into natural hazards and seismic risk. In the private sector, GPS technology is additionally used for cadastral and photogrammetric mapping surveys, definition of political-administrative limits, space analysis with thematic cartography, GIS, and land-use planning, with a wide variety of applied social, economic, and political purposes, including conservation of the environment. The city of Guadalajara and its surrounding urban area has expanded greatly in the last three decades as a result of industrial, commercial and housing activity that have substantially changed in their urban morphology. This period of unprecedented growth has occurred primarily in an unplanned and sometimes disarticulated and unbalanced manner, incongruous with the development of the most important city in western Mexico. The Department of Geography of the University of Guadalajara and the Institute of Territorial Information of the State of Jalisco (IITJ) have initiated a study of 89 geodetic sites that are located in the metropolitan zone of Guadalajara to assist in future planning and regulation of urban development, including urban and rural cadastral surveys and the establishment of diverse public services. Our work includes careful examination and evaluation of the quality and distribution of these geodetic sites with regard to anticipated growth of the metropolitan municipalities, and the vulnerability of urban zones to ground subsidence or landslides. Guadalajara is also located in a seismic zone, making precise continuous GPS measurements useful for identifying rates of strain accumulation and aseismic strain events that cannot be measured by seismographs.
G43A-02
The Plate Boundary Observatory (PBO) Network in the PNW region of the United States
The Pacific Northwest Region (PNW) of the United States contains a variety of geologic regions and tectonic
problems. These include the Cascadia Subduction Zone, Mt. St. Helens and the transition to the Basin and
Range province. Since September of 2003, the Plate Boundary Observatory (PBO), which is part of the larger
NSF-funded EarthScope project, has been installing a network of continuously operating GPS, strainmeter and
tiltmeter instruments. There are currently 78 GPS, 13 strainmeter/borehole seismometers, and 4 tiltmeters
operating in the PNW region. The data from this network has already been used to study Episodic Tremor Events
(ETS) during September 2005 and January 2007, and renewed activity on Mt. St. Helens that began on September
23, 2004. The goal is have 134 continuously operating GPS stations by the end of September 2008.
The locations of the GPS stations were determined by scientific committees. Whenever possible, multiple
instruments are deployed at the same location, and share power and communications resources. Examples of
this are GPS antennas mounted on top of strainmeter boreholes in the forearc region of western Washington and
tiltmeters collecting data through GPS receivers on Mt. St. Helens. In addition, a number of stations provide real
time kinematic data to professional surveyors within the region.
During the fall of 2006, a 16 GPS and 4 tiltmeter station network was completed on Mt. St. Helens. Results from
analysis of both PBO and USGS GPS stations on the mountain, show a radially inward and downward motion,
with the maximum vertical offsets high on the mountain and the maximum horizontal offsets located at distances
of 5-10km from the crater. Displacements are small over the 2004-present eruption with a maximum of 3cm of
inward movement. GPS stations installed high on the mountain experience severe weather and heavy rime
accumulations for approximately 6 months of the year. Ice build-up causes distortion of the GPS antenna phase
center, and sun blockages on solar panels at several sites. Due to the large battery storage capacity, there have
been very few power failures, however the build up of ice on the GPS antennas causes cm-level pseudo-
displacements that mask the ground movements associated with the eruption.
http:pboweb.unavco.org
G43A-03
A Contribution to Mitigating Seismic Risk in the Bay Area: The Bay Area Regional Deformation (BARD) GPS Network
In the San Francisco Bay Area (SFBA), two million people live in a geologically complex, tectonically active region
that has experienced several historic earthquakes, including the 1868 Hayward, the 1906 San Francisco, and
1989 Loma Prieta earthquakes. Geodetic measurements, which are especially useful for detecting deformation
and strain on deep structures throughout the seismic cycle, show that Bay Area deformation is both spatially
complex and varying with time. Increasingly, GPS data can also be used in real time to complement seismic data
in providing robust real-time earthquake information, and, potentially, early warning. The Bay Area Regional
Deformation (BARD) network of permanent, continuously operating Global Positioning System (GPS) receivers
monitors crustal deformation in the Bay Area and northern California. BARD is a network collocated with several
seismic networks (BDSN, NHFN, mini-PBO) operating in Northern California. As the local determination of
magnitude is problematic for large earthquakes, the GPS will provide strong constraints on rupture geometry and
amount of slip along the slipping fault. Thus, the collocation of all the networks will help mitigate earthquake-
related risks associated with an earthquake in the SFBA or in northern California.
http:www.ncedc.org/bard/
G43A-04
PBO Borehole Strain and Siesmic Network
UNAVCO is a non-profit, community-based organization funded by the National Science Foundation to install and operate the geodetic component of EarthScope called the Plate Boundary Observatory (PBO). UNAVCO will install 103 borehole tensor strainmeters/seismometers and 28 borehole tiltmeters These instruments will be used 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 in hopes of increasing our understanding of the causes and mechanisms associated with earthquakes and volcanic activity. This represents almost a tripling of all installed borehole strainmeters in North America. Since the initial deployment of strainmeters in the early 1980's, borehole strainmeters have contributed valuable data at periods ranging from minutes to weeks with sensitivities two to three orders of magnitude better than continuous GPS at periods of days to weeks. Borehole strainmeters have been used to image earthquakes, slow earthquakes, creep events and volcanic eruptions in the US, Iceland and Japan. A brief history of US BSM program is presented. Initial PBO strainmeter deployments show promising results: imaging two slow slip events in the PNW along with excellent tele-siesmic imaging. Exciting work has been done in the PBO community relating modeled strain from the GPS network to observed strain from the BSM network. PBO also plans the installation of three volcanic arrays at Mt St Helens, Yellowstone and Long Valley. In addition to strainmeters, each borehole contains a three-component geophone and a pore pressure transducer. A subset of the boreholes are also used for heat flow measurements. When completed the PBO borehole strainmeter network will be the largest network of strainmeters installed to date and one of the world's largest borehole seismic networks. These instruments will bridge the gap between seismology and space-geodetic techniques and represents the first dense, geographically distributed observations in this temporal regime in the US.
G43A-05
The GEORED and Plate Boundary Observatory Engineer Exchange Program
In early 2007, the Colombian Institute of Geology and Mining - INGEOMINAS initiated GEORED (Geodesia: Red de Estudios de Deformación) in order to increase the knowledge of the geodynamics of northwestern South America. GEORED is an essential tool for determining crustal deformation and is primary in the analysis of inter- plate and intraplate deformation and the present seismic cycle. Some of the objectives of the project are to improve the technical, scientific, and operational capabilities of Colombian scientists regarding tectonic and volcanic deformation in Colombia, to implement a Colombian GPS permanent network for the study of geodynamics, with near real-time data retrieval and processing, and to establish a high precision geodetic reference frame for multipurpose activities within INGEOMINAS. Phase 1 of GEORED, which includes the installation of 30 permanent GPS stations in Colombia, will commence in early 2007. The Plate Boundary Observatory (PBO), part of the larger NSF-funded EarthScope project managed by UNAVCO, will study the three-dimensional strain field resulting from active plate boundary deformation across the Western United States. PBO is a large construction project involving the reconnaissance, permitting, installation, documentation, and maintenance of 875 permanent GPS stations scheduled for completion in September 2008. PBO is currently in the fourth year of the project, with over 550 GPS stations completed to date. INGEOMINAS recently became a member of the UNAVCO consortium. UNAVCO has been working with INGEOMINAS by providing technical support for the GEORED project relating to GPS receiver specifications. In the spirit of collaboration and outreach, INGEOMINAS and UNAVCO will begin an engineer exchange program starting in early summer 2007. The purpose of this outreach program is to provide a mechanism for the exchange of ideas relating to GPS station construction techniques, hardware designs, data communications, and data archiving based upon the UNAVCO PBO experience and based upon the extensive INGEOMINAS experience in installing scientific instrumentation in remote locations and difficult conditions. The Plate Boundary Observatory and GEORED will provide a natural laboratory for training in GPS construction techniques.