Broadband source spectrum, seismic energy, and stress drop of the 1989 Macquarie Ridge earthquake

Journal Article · Fri Jun 01 00:00:00 EDT 1990 · Geophysical Research Letters (American Geophysical Union); (USA)

DOI:https://doi.org/10.1029/GL017i007p01021· OSTI ID:6148298

Houston, H ^[1]

---

1. Univ. of California, Santa Cruz (USA)

The author computes the broadband source spectrum at periods from 1 to 50 seconds using teleseismic P body waves of the May 23, 1989 Macquarie Ridge earthquake (M{sub W} = 8.1) recorded by the GDSN, GEOSCOPE, and IDA networks. The average source spectrum is obtained by windowing, tapering, and Fourier-transforming P waves, removing from the spectra the effects of attenuation, geometrical spreading, and radiation pattern, and averaging logarithmically over the stations. The source spectrum for the strike-slip Macquarie Ridge earthquake is higher than an average source spectrum of seven recent large earthquakes (scaled to be comparable to a M{sub W} = 8.1 earthquake) by a factor of 2 to 3 at periods of 1 to 20 seconds. These other earthquakes were underthrusting events in subduction zones. Using Haskell's formulation assuming a point source with no directivity, she estimates the seismically radiated energy from the source spectrum by integrating the square of the source spectrum in velocity and scaling the result. The seismic energy thus estimated for the Macquarie Ridge earthquake is 3 to 8 {times} 10{sup 23} ergs. An Orowan stress drop can be obtained from the seismic energy and moment. The Orowan stress drop for the Macquarie Ridge earthquake is about 20 to 50 bars, much higher than similarly determined stress drops of other recent large earthquakes. There is a correlation between the Orowan stress drops and time since the last earthquake of comparable or larger magnitude for seven recent large earthquakes. This correlation suggests that a healing process operates that may control the mechanical strength of the fault and is important on time scales of tens to hundreds of years.

• OSTI ID: 6148298
• Journal Information: Geophysical Research Letters (American Geophysical Union); (USA), Vol. 17:7; ISSN 0094-8276
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
EARTHQUAKES
DATA ANALYSIS
NEW ZEALAND
CALCULATION METHODS
EARTHQUAKE MAGNITUDE
FOURIER TRANSFORMATION
GEOLOGIC FAULTS
ROCK MECHANICS
SEISMIC EFFECTS
SEISMIC P WAVES
SEISMIC WAVES
STRESS ANALYSIS
AUSTRALASIA
GEOLOGIC FRACTURES
GEOLOGIC STRUCTURES
INTEGRAL TRANSFORMATIONS
MECHANICS
SEISMIC EVENTS
TRANSFORMATIONS
580000* - Geosciences