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Depth estimates of large earthquakes on the Island of Hawaii since 1940

Eissler, Holly K. and Kanamori, Hiroo (1986) Depth estimates of large earthquakes on the Island of Hawaii since 1940. Journal of Geophysical Research B, 91 (B2). pp. 2063-2076. ISSN 0148-0227. doi:10.1029/JB091iB02p02063.

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Although hypocenters of earthquakes on the island of Hawaii are now routinely assigned to within 5 km, depth was a poorly determined parameter until the early 1960's. However, the 1950–1960 period was very active both in volcanic eruptions and large earthquakes. Source depths for the 12 largest Hawaiian earthquakes (magnitude 6 or greater) since 1940 are estimated from the ratios of body and surface wave amplitudes recorded at Pasadena, California. Excitation functions for Rayleigh waves are calculated as a function of source depth for the two dominant periods in the Pasadena records, 8s and 20s. Theoretical body wave amplitudes are determined from synthetic seismograms. Calculated ratios are very sensitive to source depth; for example, amplitudes of 8-s Rayleigh waves diminish by a factor of 300 between depths of 10 km and 50 km. This is a much larger effect than the fault geometry, which we estimate to be a factor of 4 between representative focal mechanisms. Estimated depths for post-1960 earthquakes agree fairly well with the instrumental depths. In general, large earthquakes near the volcanic flanks and fault systems are shallow (≤20 km). Two earthquakes of magnitude 6 occurred under the volcanoes Mauna Loa (in 1950) and Kilauea (in 1951); they preceded major eruptions by 3 days and 14 months, respectively, and had the largest depth estimates at 40–55 km and 35–50 km. MS values assigned from global amplitudes are compared with those assigned from Pasadena amplitudes alone, for 70 events in 1973–1974 with 5.1≤ M_S ≤ 6.0. The global values are only slightly larger (0.05 magnitude units) than the Pasadena values, indicating that Pasadena amplitudes are on the average representative of the event magnitude.

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Kanamori, Hiroo0000-0001-8219-9428
Additional Information:© 1986 American Geophysical Union. Paper number 4B5311. Received October 16, 1984; revised June 28, 1985; accepted August 23, 1985. We would like to thank Jim Westphal of the California Institute of Technology for first calling our attention to the 1950 Mauna Loa earthquake. We thank Elliot Endo of the Cascades Volcano Observatory and Robert Koyanagi of the Hawaiian Volcano Observatory for discussion of Hawaiian seismicity and preliminary information on the 1983 Kaoiki earthquake and 1984 eruption of Mauna Loa. One of us (H.K.E.) is grateful to R. P. Sharp and the donors to Caltech's 1985 Project Pahoehoe for the opportunity to see the geology of Hawaii firsthand. This research was supported by the Earth Sciences Section, National Science Foundation, grant EAR-8313223. Contribution 4149, Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California.
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Caltech Division of Geological and Planetary Sciences4149
Issue or Number:B2
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Official Citation:Eissler, H. K., and H. Kanamori (1986), Depth estimates of large earthquakes on the Island of Hawaii since 1940, J. Geophys. Res., 91(B2), 2063–2076, doi:10.1029/JB091iB02p02063
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:51248
Deposited By: Tony Diaz
Deposited On:04 Nov 2014 22:32
Last Modified:10 Nov 2021 19:08

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