Fault-zone attenuation of high-frequency seismic waves
- Univ. of California, Santa Barbara (USA)
The authors have developed a technique to measure seismic attenuation within an active fault-zone at seismogenic depths. Utilizing a pair of stations and pairs of earthquakes, spectral ratios are performed to isolate attenuation produced by wave-propagation within the fault-zone. The empirical approach eliminates common source, propagation, instrument and near-surface site effects. The technique was applied to a cluster of 19 earthquakes recorded by a pair of downhole instruments located within the San Andreas fault-zone, at instruments located within the San Andreas fault-zone, at Parkfield, California. Over the 1-40 Hz bandwidth used in this analysis, amplitudes are found to decrease exponentially with frequency. Furthermore, the fault-zone propagation distance correlates with severity of attenuation. Assuming a constant Q attenuation operator, the S-wave quality factor within the fault-zone at a depth of 5-6 kilometers is 31 (+7,{minus}5). If fault-zones are low-Q environments, then near-source attenuation of high-frequency seismic waves may help to explain phenomenon such as f{sub max}. Fault-zone Q may prove to be a valuable indicator of the mechanical behavior and rheology of fault-zones. Specific asperities can be monitored for precursory changes associated with the evolving stress-field within the fault-zone. The spatial and temporal resolution of the technique is fundamentally limited by the uncertainty in earthquake location and the interval time between earthquakes.
- OSTI ID:
- 5542126
- Journal Information:
- Geophysical Research Letters (American Geophysical Union); (USA), Vol. 16:11; ISSN 0094-8276
- Country of Publication:
- United States
- Language:
- English
Similar Records
I. Seismotectonics of the San Jacinto fault zone and the Anza seismic gap. II. Imaging the shallow crust in volcanic areas with earthquake shear waves
Earthquake travel time tomography of the southern Santa Cruz Mountains: Control of fault rupture by lithological heterogeneity of the San Andreas fault zone
Related Subjects
GEOLOGIC FAULTS
RESPONSE FUNCTIONS
SEISMIC WAVES
ATTENUATION
AMPLITUDES
CALIFORNIA
DATA ANALYSIS
DEPTH
EARTHQUAKES
FREQUENCY DEPENDENCE
MEASURING METHODS
MECHANICAL PROPERTIES
RHEOLOGY
DEVELOPED COUNTRIES
DIMENSIONS
FEDERAL REGION IX
FUNCTIONS
GEOLOGIC FRACTURES
GEOLOGIC STRUCTURES
NORTH AMERICA
SEISMIC EVENTS
USA
580000* - Geosciences