Geology topics
T. Holzer
Publications and source records attributed to T. Holzer.
Strong-motion, site-effects and hazard issues in rebuilding Turkey: In light of the 17 August, 1999 earthquake and its aftershocks
The August 17, 1999 Izmit (Turkey) earthquake (Mw=7.4) will be remembered as one of the largest earthquakes of recent times that affected a large urban environment (U.S. Geological Survey, 1999). The shaking that caused the widespread damage and destruction was recorded only by a handful of accelerographs in the earthquake area operated by different networks. The characteristics of these records show that the recorded peak accelerations, even those from near field stations, are smaller than expected. On the other hand, smaller magnitude aftershocks yielded larger peak accelerations. This is attributed to the sparse networks, which possibly missed recording of larger motions during the main shock. As rebuilding of Turkey starts, strong-motion networks that yield essential data must be enlarged. In addition, attention must be paid to new developments elsewhere, such as earthquake zoning maps, earthquake hazard maps, liquefaction potentials and susceptibility. This paper aims to discuss these issues. Copyright??2000 IAHS.
Land subsidence caused by the East Mesa geothermal field, California, observed using SAR interferometry
Interferometric combination of pairs of synthetic aperture radar (SAR) images acquired by the ERS-1 satellite maps the deformation field associated with the activity of the East Mesa geothermal plant, located in southern California. SAR interferometry is applied to this flat area without the need of a digital terrain model. Several combinations are used to ascertain the nature of the phenomenon. Short term interferograms reveal surface phase changes on agricultural fields similar to what had been observed previously with SEASAT radar data. Long term (2 years) interferograms allow the study of land subsidence and improve prior knowledge of the displacement field, and agree with existing, sparse levelling data. This example illustrates the power of the interferometric technique for deriving accurate industrial intelligence as well as its potential for legal action, in cases involving environmental damages.
Faulting arrested by control of ground-water withdrawal in Houston, Texas
More than 86 historically active faults with an aggregate length of 150 miles have been identified within and adjacent to the Houston, Texas, metropolitan area. Although scarps of these faults grow gradually and without causing damaging earthquakes, historical fault offset has cost millions of dollars in damage to houses and other buildings, utilities, and highways that were built on or across the faults. The historical fault activity results from renewed movement along preexisting faults and appears to be caused principally by withdrawal of ground water for municipal, industrial, and agricultural uses in the Houston area. Approximately one-half of the area's water supply is obtained from local ground water. Monitoring by the US Geological Survey of heights of fault scarps indicates that many of the scarps have recently stopped increasing in height. The area where faulting has ceased coincides with the area where ground-water pumping was cut back in the mid-1970s to slow the damage caused by land subsidence along Galveston Bay and the Houston Ship Channel. Thus, it appears that efforts to halt land subsidence in the coastal area have provided the additional benefit of arresting damaging surface faulting. -from Authors