Empirical Green's functions from small earthquakes: A waveform study of locally recorded aftershocks of the 1971 San Fernando earthquake

Journal Article · Sat Feb 10 04:00:00 EST 1990 · Journal of Geophysical Research; (United States)

DOI:https://doi.org/10.1029/JB095iB02p01187· OSTI ID:5009306

Hutchings, L; Wu, F ^[1]

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1. State Univ. of New York, Binghamton (United States)

Seismograms from 52 aftershocks of the 1971 San Fernando earthquake recorded at 25 stations distributed across the San Fernando Valley are examined to identify empirical Green's functions, and characterize the dependence of their waveforms on moment, focal mechanism, source and recording site spatial variations, recording site geology, and recorded frequency band. Recording distances ranged from 3.0 to 33.0 km, hypocentral separations ranged from 0.22 to 28.4 km, and recording site separations ranged from 0.185 to 24.2 km. The recording site geologies are diorite gneiss, marine and nonmarine sediments, and alluvium of varying thicknesses. Waveforms of events with moment below about 1.5 {times} 10{sup 21} dyn cm are independent of the source-time function and are termed empirical Green's functions. Waveforms recorded at a particular station from events located within 1.0 to 3.0 km of each other, depending upon site geology, with very similar focal mechanism solutions are nearly identical for frequencies up to 10 Hz. There is no correlation to waveforms between recording sites at least 1.2 km apart, and waveforms are clearly distinctive for two sites 0.185 km apart. The geologic conditions of the recording site dominate the character of empirical Green's functions. Even for source separations of up to 20.0 km, the empirical Green's functions at a particular site are consistent in frequency content, amplification, and energy distribution. Therefore, it is shown that empirical Green's functions can be used to obtain site response functions. The observations of empirical Green's functions are used as a basis for developing the theory for using empirical Green's functions in deconvolution for source pulses and synthesis of seismograms of larger earthquakes.

• OSTI ID: 5009306
• Journal Information: Journal of Geophysical Research; (United States), Journal Name: Journal of Geophysical Research; (United States) Vol. 95:B2; ISSN 0148-0227; ISSN JGREA
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580000* -- Geosciences
AFTERSHOCKS
CALIFORNIA
DEVELOPED COUNTRIES
EARTHQUAKES
EQUATIONS
FEDERAL REGION IX
FREQUENCY DEPENDENCE
FUNCTIONS
GEOLOGY
HYPOCENTERS
MEASURING INSTRUMENTS
MECHANICS
NORTH AMERICA
RESPONSE FUNCTIONS
ROCK MECHANICS
SEISMIC ARRAYS
SEISMIC DETECTORS
SEISMIC EVENTS
SEISMIC SOURCES
SEISMOGRAPHS
SPACE DEPENDENCE
USA
WAVE FORMS