The Loma Prieta Earthquake, 1989 and Earth strain tidal amplitudes: An unsuccessful search for associated changes

Abstract

The Loma Prieta earthquake of 1989 provided an opportunity for a sensitive test of suggestions that earthquakes may be preceded by variations in Earth tidal strain amplitudes. Such variations have been proposed as providing an advantageous technique for detecting precursory changes in elastic parameters in a seismogenic zone. We have analyzed data from two borehole strainmeters continuously operating within 40 km of the epicenter and within about 10 km of the southern end of the rupture. We are unable to identify any precursory changes in M2 and O1 tidal amplitudes and estimate that any large scale changes in Young's modulus must have been less than about 2%. If these results apply generally, we would conclude that variations in elastic material properties prior to earthquakes do not occur throughout substantial volumes of the subsequent hypocentral region.

Disruption of groundwater systems by earthquakes

“…Since ρ and g do not change with earthquake, the coseismic increase in H implies a coseismic increase in BK u ε . Moreover, measurements of strains in the near fields of two large earthquakes [ Linde et al ., ; Johnston et al ., ] revealed no detectable (<5%) coseismic change of the amplitude of the M2 tidal volumetric strain ( ε ). If this result can be generalized to the Jiangyou well, the coseismic increase in H at Jiangyou well (~30%) implies a coseismic increase in BK u .…”

Earthquake prediction: a critical review

“…However, the geyser is at an epicentral distance of 177 km. High-quality strain measurements at distances of only several tens of kilometres were uneventful (Johnston 1993, p. CI), and changes in material properties, as indicated by the response to Earth tides, were absent (Linde, Gladwin & Johnston 1992) . Silver & Valette-Silver (1992, p. 1367) rejected the possibility that the pre-seismic variations were due to chance coincidence.…”