In-place calibration of USGS pore pressure transducers at Wildlife Liquefaction Site, California, USA

Abstract

Acceleration and pore-pressure data were recorded at the Wildlife Site during the magnitude 6.6 Imperial Valley earthquake of 24 November 1987 which resulted in liquefaction of the site, alone among instrumented sites. Some unusual aspects were observed in the data, including long rise times of the pore pressures resulting in a time lag between the strong ground shaking and maximum pore pressure development. It was not clear from the data obtained whether the liquefaction process at the Wildlife Site was different from that observed in other saturated sand deposits, or if the pore-pressure transducers were not responding correctly. In December 1989, the authors performed an in-situ dynamic calibration of the USGS piezometers installed at the Wildlife Site with respect to reference pore-pressure transducers showing that only one of the transducers was performing nearly correctly. Several hypotheses have been examined to explain the data recorded during the earthquake, including particularly transducer malfunction due to air bubbles in the transducer chambers.