Earthquake Engineering Group (EEG) Data Center
The geotehnical array data portal, maintained at ERI, receives data streams from several remote field sites (more information in the section below). These sites, equipped with seismic sensors for monitoring ground shaking, pressure sensors for monitoring liquefaction, and video telepresence cameras, deliver their data via secure VPN routers connecting the radio-based wireless field network to the local ERI network servers. The data portal server provides researchers worldwide with access to the earthquake data via web-based search and download access (www.nees.ucsb.edu/data-portal). The real-time streaming data is also forwarded on to other regional seismic monitoring networks and national data centers.
Instrumentation and Seismic Observatories Programs at ERI
ERI is home to significant instrumentation and research efforts focused on understanding the physics of the earthquake process and the effects of earthquakes on the built environment. These require not only computational facilities for doing theoretical modeling of wave propagation and earthquake source process simulation, but also field observatories for monitoring earthquake activity. These field observatories provide the control data for testing our theoretical models and simulation techniques in order to allow us to determine if our models are matching real observations of earthquakes.
ERI operates a number of field facilities for monitoring earthquakes. The cost of installing and operating both portable instrumentation and permanent field sites can be quite high, so these costs are shared by many funding agencies. Currently, the largest field monitoring program at ERI is supported through the support from Pacific Gas & Electric Corporation (PG&E) and the United States Geological Survey (USGS). This program was previously funded through the U.S. Nuclear Regulatory Commission (NRC), and prior to that from the National Science Foundation (NSF) Engineering Directorate's George E. Brown Jr., Network for Earthquake Engineering Simulation (NEES) program. Support from NSF's Earth Sciences directorate and the U.S. Geological Survey through the Southern California Earthquake Center provide support for the Portable Broadband Instrument Center (PBIC) and the Borehole Instrumentation Program. These combined resources as well as local institutional resources and in-kind support from other agencies are used to maintain the overall instrumentation and seismic observatories program at ERI.
Portable Broadband Instrument Center
The Portable Broadband Instrument Center (PBIC) was established in 1991 by the Southern California Earthquake Center (SCEC) to provide researchers in southern California with year-round access to a "pool" of portable seismic recording equipment. The PBIC maintains this equipment and also serves as a Rapid Array Mobilization Program (RAMP) facility in the event of significant earthquakes. At other times PBIC equipment is used on projects related to SCEC science and data gathering goals. The PBIC is managed out of ERI by Principal Investigator Jamie Steidl.
The first generation of data recorders maintained by the PBIC were primarily Refraction Technology (RefTek) 16 and 24 bit data acquisition systems (DAS's). These have now beind phased out and are slowly being replaced with modern network aware 24-bit Quanterra Q330 and Kinemetrics Rock Platform DAS's. Sensors consist of high output short period velocity transducers to record very small ground motion, force balance accelerometers designed to stay on-scale (up to +-2G) for the strong ground motion expected from very large earthquakes, and intermediate period weak motion sensors that provide increased frequency bandwidth to allow better investigation of deep basins and teleseismic or global earthquake monitoring. A broad dynamic range of recording is obtained by pairing both weak motion and strong motion sensors with a single DAS.
As we bring online the next generation dataloggers, the combination of these new dataloggers and sensors allows recording from as low as M1 earthquakes all the way to M8+ earthquakes on scale. In addition, these stations have the capability to stream the data continuously back to UCSB and the regional monitoring networks in real-time. The data is then integrated into the network processing routines, used for locating earthquakes, calculating magnitudes, and producing shake maps for emergency response for the larger events. Then the data is archived along with the permanent network data and made accessible through the regional data centers.
Geotechnical Array Monitoring
Permanently instrumented field sites for geotechnical array monitoring represent one of the major focuses of the EEG at UCSB. The overarching goal of the this field site monitoring program is to improve on our ability to generate analytical and empirical models for accurate simulation of how the ground responds and deforms when shaken by earthquakes and to understand how this seismically induced shaking affects building structures and foundations. Two complimentary approaches have been developed: Continuous monitoring of natural earthquakes with down-hole seismometers and pore pressure transducers, and the use of large "mobile shakers" to allow active shaking of both structures and the nearby ground during controlled experiments.
The Garner Valley field site:
The Garner Valley Downhole Array (GVDA) is a field site located in a seismically active region of California, 7 km from the San Jacinto fault and 35 km from the San Andreas fault. The site is situated in a narrow valley within the Peninsular Ranges Batholith 23 km east of Hemet and 20km southwest of Palm Springs, California. A one-story soil-foundation structure-interaction (SFSI) structure was constructed at the site for the study of dynamic response of this structure during earthquakes. The site has been thoroughly characterized through borehole geotechnical tests and in other studies over the last 25 years. Instrumentation of the GVDA site began in 1989 and has continued to expand in scope since the initial installation.
The near-surface stratigraphy beneath GVDA consists of 18-25 m of lake-bed alluvium. Soil types present are silty sand, sand, clayey sand, and silty gravel. The alluvium gradually transitions into decomposed granite in the depth interval between 18 m to 25m. Decomposed granite consisting of gravely sand exists between 25 and 88 meters. At ~88 meters the contact with granodiorite of the Southern California Peninsular Ranges batholith is reached.
The Garner Valley site is very well suited to the study of soil-foundation-structure interaction and liquefaction. The area is located near several active faults on low density alluvial soil with a near surface water table. The water table fluctuates at the GVDA site depending on the season and rainfall totals. In the wetter years the water table is at, or just below the surface in the winter and spring months. In the summer and fall months, or the entire dry years, the water table drops to 1 to 3 meters below the surface. Pressure transducers within the liquefiable sediments, and accelerometers at the surface and at various depths within the soil column and in the bedrock below are all monitored continuously in real-time, and the data archived both locally on-site and at UCSB. Over 6,000 Magnitude 1 and larger earthquakes have beed observed at the GVDA facility since 1989. Data from the GVDA site can be found at the UCSB data portal (www.nees.ucsb.edu/data-portal).
The Garner Valley Soil-Foundation-Structure Interaction (SFSI) test facility is composed of a medium-scale reconfigurable steel-frame structure founded on a rigid, massive concrete slab on grade. Shakers can be mounted on the roof for active experiments to complement passive earthquake monitoring. The test structure is densely instrumented and also monitored continuously in real-time.
The Wildlife Liquefaction Array field site:
The Wildlife Liquefaction Array (WLA) is a ground motion monitoring and liquefaction research site. Located at the southern most terminus of the San Andreas Fault system, the WLA field site records multiple earthquakes daily in this seismically active area. WLA is situated in California's Imperial Valley on the west bank of the Alamo River 13 km due north of Brawley, California and 160 km due east of San Diego. Records from WLA provide essential information to scientists who study ground response, ground failure, and liquefaction. Predicting these effects using computer models requires instrumented field sites to validate the simulation methods against real observations. Instrumentation of the site began in 1982 by the US geological Survey, was upgraded in 2004 through the NEES program, and monitoring and data analysis continues today through support from the US NRC.
The near-surface geology of the WLA site consists of a 2.5 to 3.0m thick layer of silty clay to clayey silt caps the site. This layer is underlain by a 3.5 to 4.0m thick granular layer composed of silt, silty sand, and sandy silt. The granular layer is underlain by a thick layer of silty clay to clay.
The confined silty sand layer, from approximately 3 - 7 m, is highly susceptible to increases in pore pressure and potential liquefaction and a major reason for selecting this site for instrumentation Six events in the past 75 years have generated liquefaction effects within 10 km of the WLA site. Researchers are using earthquakes that occur on a daily basis near this site, as well as active testing using mobile shakers, to try and better understand how near-surface geologic conditions affect ground shaking.
Like the GVDA site, pressure transducers within the liquefiable sediments, and accelerometers at the surface and at various depths within the soil column down to 100 meters depth are all monitored continuously in real-time, and the data archived both locally on-site and at UCSB. Over 9,000 Magnitude 1 and larger earthquakes have beed observed at the GVDA facility since 2004, when the NEES program began. Data from the WLA site can be found at the UCSB data portal (www.nees.ucsb.edu/data-portal).
The Borrego Valley Downhole Array:
In 1993, Kajima Engineering and Construction Corp. and Agbabian Associates established the Borrego Valley downhole array (BVDA) near Borrego Springs, in Southern California. In this array there are four borehole instruments extending to depths of 9, 19, 139 and 238 m. In addition, BVDA has ~10 surface instruments extending in two directions across the Borrego Valley, and a remote rock site at the edge of the valley that includes surface and borehole sensors. At the main station data acquisition systems building the shear wave velocity gently increases from about 300 m/s at the surface to 750 m/s at 230 m-the granite interface-where it jumps to 2500 m/s. The water table is at ~92 m; BVDA is representative of a dry site in NEHRP site class C.
The BVDA site is complementary to the NEES facilities in that it represents a different soil condition (dry vs. wet) and slightly stiffer material properties. It is important to collect data from all of the soil conditions encountered in the built environment in order to test our simulation methods using different soil models. Data from the BVDA site can be found at the UCSB data portal (www.nees.ucsb.edu/data-portal).
The Hollister Earthquake Observatory:
Agbabian Associates installed the Hollister Earthquake Observatory (HEO) in 1991 with funding from the Kajima Engineering and Construction Corporation. Kajima Corporation donated this array to the University of California, Santa Barbara in January 1998. It is located in the Salinas Valley where alluvium overlies Tertiary sandstone overlying Granitic basement. HEO has been operating since early 1992, and is located about 10 kilometers from the San Andreas Fault near the cities of Hollister and Salinas in central California. The ground motion array consists of a vertical array of six accelerometers in Quaternary alluvium, and three accelerometers installed at a remote rock station, 3 km to the Northeast. At the HEO main soil station accelerometers are located at 192, 110, 50, 20, 10, and 0 meters depth, going from crystalline rock at the bottom, up through consolidated and unconsolidated alluvium to the surface. Three sensor locations, surface Sandstone, surface Granite, and GL-53 meter borehole Granite are instrumented at the remote rock station. The location of HEO along the San Andreas Fault in Central/Northern California makes it an important addition to UCSB's seismological monitoring field site programs. Data from the HEO site can be found at the UCSB data portal (www.nees.ucsb.edu/data-portal).
The SCEC Borehole Instrumentation Program:
The Southern California Earthquake Center, with funding from the USGS and NSF, has supported the instrumentation and maintenance of borehole and surface instruments at locations throughout southern California for the past two decades. These stations are collaborative with the regional networks, and typically include just a surface and single borehole sensor, with the data streaming directly to the regional networks, and archived at the Southern California Earthquake Data Center (www.data.scec.org). The borehole network consists of 18 stations funded through cost sharing between SCEC and EarthScope, CGS, USGS/Caltech, Caltrans, and the NRC. The instrumentation is used to gain a better understanding of the near-surface effects on ground motions, to improve our ability to account for these effects in simulations of ground motion, and to get a more detailed observation of the earthquake source by avoiding the near-surface layers that typically attenuate high-frequency radiation. Recently we have begun to integrate the data from these borehole stations into the geotechnical array data portal (www.nees.ucsb.edu/data-portal).