PS46, Lajitas, Texas, United States
Thumbnail Profile: West Texas
The region which is today West Texas, USA, was inhabited by nomadic Native American tribes such as the Apache, Comanche and Kiowa until after the 1860s Civil War. Today there is a substantial Hispanic population, especially near the Rio Grande border between Mexico and the United States. Many Mexicans fled to Texas during the Mexican Revolution in the early years of the 20th century and still retain close family ties in their country of origin.
El Paso, a commercial, university and military town with a population of some 625,000 people, is largest city in West Texas. It borders on the U.S. state of New Mexico to its west and the country of Mexico to the south. West Texas is remote and has a much lower population density than the rest of the state.
With its sparsely populated and relatively unpolluted land and its wide open spaces, West Texas has also become a destination for people seeking respite from busy urban life. The region has recently become known for is numerous wind turbine generators that produce pollution-free electricity.
Geography and Climate
Geographically, West Texas has more in common with the Southwestern United States than it does with the rest of the state of Texas. Well-known for its natural beauty and many small mountain ranges, much of southern West Texas west of the Pecos River belongs to the Chihuahuan desert.
This part of Texas has a climate that many find pleasant: cold nights contrasting with warm afternoons in winter; hot days contrasting with refreshingly cool nights in the summer.
Because this semi-arid climate receives far less rainfall than the rest of the state, West Texas is heavily dependent on irrigation to support its agricultural sector. Water siphoned off farther north to meet the urban needs means that both the Pecos River and the once mighty Rio Grande have been reduced at times to little more than a trickle.
The United States hosts more IMS facilities than any other CTBT Member State: these include four other primary stations in addition to PS46, 12 auxiliary seismic stations, two hydroacoustic stations, eight infrasound stations, 11 radionuclide stations and one radionuclide laboratory.
The Lajitas seismic array (PS46) station is located in scenic southwestern Texas close to Big Bend National Park and 16 km northeast of the small village of Lajitas on the Rio Grande River. The relative remoteness of the station allows for precise seismic measuring results.
All elements of the primary seismic array are located in the Cretaceous Santa Elena Formation (massive limestone). Located in a region consisting of ridges and valleys with vegetation comprising cactai and low shrubs typical of dry Southwestern desert climates, the array is accessible at all times of the year, which is an advantage for servicing and repair. Average temperatures range from nighttime lows of -3ºC in winter to daytime highs of +36ºC in summer; snow is virtually unknown. This unmanned IMS station is operated remotely by Southern Methodist University (SMU) in Dallas, Texas.
PS46’s first array—a spatially distributed set of seismometers all transmitting their outputs to a Central Recording Facility (CRF) where they are recorded, was constructed in 1980 and upgraded in 1988.
In 1993 the original nine-element array was completed. In 1999 the data acquisition system was further upgraded. Data authentication—that is, measures to ensure that the integrity of the International Monitoring System (IMS) data has not been compromised—was added to the array, and upgraded software was installed during 2001 prior to the station’s certification in December of that year.
The United States pays all the operating costs for this station, and the only direct involvement of CTBTO’s Provisional Technical Secretariat in the construction of PS46 was the purchase of Science Horizons data authenticators. Today PS46 is a regional array with 12 physical elements that cover an area of about three kilometres.
Testing, Evaluation and Certification
Towards the end of 2001, PS46 was shown to meet all of the Preparatory Commission for the Comprehensive Nuclear-Test-Ban Treaty Organization's (CTBTO) certification requirements.
Data authentication devices and Global Communications Infrastructure (GCI) were in place and had been demonstrated to work properly. The station had performed at a high (average 98% or more) data availability rate and the data, sent to the International Data Centre (IDC) via the United States’ independent sub-network, had been used successfully in the IDC Processing for a substantial time.
The station had a good long-term performance record and a competent operations and maintenance staff. Consequently, this station was certified on 20 December 2001.