Geophysical and Hydrologic Prediction of Fissuring and Land Subsidence, South-Central Arizona

摘要

Bimonthly horizontal strain measurements of fissures have been made at seven dial gauges near Signal Peak, Picacho Mountains, and in Avra Valley, Arizona. A Pyrex glass rod is fixed on one side of a fissure and pushes against a dial gauge fixed to the other side. Installations are in shallow covered trenches. Movements ranging from 5 micrometers to 25 mm are detected with a measurement error of less than 5 micrometers. Fissures have been observed to open and close repeatedly. With one exception, old and new cracks showed no pronounced difference in character. Following a severe storm, one fissure abruptly opened 31 mm within a 14-hour period while one nearby parallel fissure opened 1.6 mm and another nearby parallel fissure closed 2.1 mm. Correlation of fissure movement, rainfall, pumping, and water-level fluctuations indicates that major earth fissure movements will occur after high pumping rates during or shortly after large storms. The authors long term records will form the data base for predictive models of subsidence and earth fissuring.