News Release

Scientists at The University of Texas Institute for Geophysics (UTIG) have measured the recent earthquake in Taiwan that measured 7.6 on the Richter scale at their seismic station in Hockley Texas. The Hockley seismic station (station code HKT) is one of two modern 3-component broadband digital seismometers operating in Texas. The seismic energy released by an earthquake recorded at Hockley is encoded and the data are sent via satellite to the data processing system located in the main computer room at UTIG in Austin. This permits UTIG researchers to monitor earthquakes within seconds of their arrival time signals. Data acquired from Hockley are forwarded to the Global Seismic Network (GSN), operated by the Incorporated Research Institutions for Seismology (IRIS). The Hockley seismic station is also a cooperating member of the United States National Seismic Network (USNSN) maintained by the USGS. The Hockley seismometer is located in a chamber 470 meters below the surface in an active salt mine owned by United Salt Corporation. Locating the instrument within a salt dome reduces the noise from human activity and natural disturbances (i.e.wind) that affect instruments on the surface.

The Taiwan earthquake occurred along a tectonic plate boundary zone that marks the collision of the Philippine Sea, a western segment of the Pacific Ocean, with the mainland of Asia. Here a volcanic arc is being smashed against the Asian continent resulting in earthquakes, uplift, and mountain building. Taiwan, in fact, is actually a product of the intense geologic activity associated with this collision. The Taiwan earthquake is of particular importance to UTIG scientists Drs. Yosio Nakamura and Kirk McIntosh who, since 1995, have collaborated with other scientists from the United States and Taiwan to study the tectonic and mountain building processes associated with the Taiwan arc-continent collision. The UTIG team carried out a program of seismic refraction experiments using a suite of Ocean Bottom Seismographs (OBS). The OBS instruments are specially designed and built at UTIG to be placed on the seafloor to record seismic events. The work was carried out using two research ships: (1) the R/V Ocean Researcher I of the National Taiwan University and (2) the R/V Maurice Ewing, named after the Texan founder of the Institute for Geophysics.

BACKGROUND
The Hockley Seismic Station The Hockley seismometer consists of three Streckeisen STS-1 sensors oriented vertically, north-south, and east-west, mounted on a concrete slab, and kept in evacuated containers. The seismic sensors feed a signal directly to the data acquisition (DA) unit. The heart of the DA is a Motorola VME-147s computer running OS-9 system software. A fiber optic cable connects the DA to VSAT communications hardware, a GPS clock, and a dial-up modem on the surface. Using the VSAT link, the data stream travels to the National Earthquake Information Center (NEIC) in Golden, Colorado, where the USNSN monitors national earthquake activity. The NEIC then transmits the seismometer data via satellite to the data processing (DP) system located in the main computer room at UTIG in Austin.

OCEAN-BOTTOM SEISMOGRAPH
 UTIG has developed a specialized ocean-bottom seismomograph (OBS). This is a microprocessor-controlled instrument that is placed on the seafloor to record seismic signals generated by seismic sources. The OBS instrument and control electronics are contained in a glass ball encased in a yellow polyethylene housing (sphere) called a hard hat. The instrument is deployed from a surface ship, free-falls to the seafloor, and while on the seafloor detects and records seismic signals. Commercially available hard disks store the data in the instrument. Experiments may be passive, in which the energy generated by earthquakes is detected and used to create an image of the Earth’s interior, or active, in which a sesimic source (i.e. sound) is generated from research ships. After the data acquisition is completed, the system receives a sound signal from a surface ship, which triggers the OBS to release itself from the seafloor and float to the surface for recovery. On board the ship, the data can be downloaded to standard computer workstations and evaluated. UTIG researchers are currently using OBS instruments in offshore seismic investigations with diverse geological/geophysical targets in many parts of the world.

Taiwanese scientists are currently using OBS instruments based on the UTIG design, and built with the assistance of Dr. Yosio Nakamura, to record offshore earthquakes.

For more information, please contact any one of the following:

Dr. Clifford Frohlich 512-232-3260
Dr. Yosio Nakamura 512-232-3392
Dr. Jay Pulliam 512-232-3296
Dr. Katherine Ellins (UTIG Program Manager) 512-232-3251