Journal of Natural Disaster Science

SEARCH FOR THE BURIED SUBFAULT(S) OF THE 16 JULY 1990 LUZON EARTHQUAKE, THE PHILIPPINES USING AFTERSHOCK OBSERVATIONS

Takuo SHIBUTANI*, Takahiro OHKURA**, Yoshihisa IIO*, Masaki KANAO*, Kin'ya NISHIGAMI*, Koji TASAKI*, Tomotaka IWATA*, Yasumaro KAKEHI*, Norio HIRANO*, Masataka ANDO*, Bartolome C. BAUTISTA***, Jesus R. PUERTOLLANO***, Angelito G. LANUZA***, Arnold A. MELOSANTOS***, Arnold CHU***, Ronald PIGTAIN***, Edwin dela CRUZ*** and Raymundo S. PUNONGBAYAN***
* Disaster Prevention Research Institute, Kyoto University
** College of Liberal Arts and Science, Kyoto University
*** Philippine Institute of Volcanology and Seismology

(Received 15 April 1991 and in revised form 4 September 1991)

Abstract

Two aftershock observations were made for the 16 July 1990 Luzon earthquake (Ms=7.8). The first was made at twelve stations from Aug. 30 to Sep. 4. The temporary stations were set around the area of ground rupture and in the environs of Baguio City which experienced severe damage. Although the observation period was short, many aftershocks were recorded and 139 hypocenters were located. The aftershock distribution indicates two distinct clusters; one along the fault of the main shock and the other in an area west, northwest of Baguio City. The latter cluster suggests the existence of a subfault (s) beneath the area around Baguio City.

The second aftershock observations were made from Nov. 17 to Dec. 7. Seven stations were set, of which five were concentrated in the area around Baguio City in order to accurately determine the location of aftershocks in this region. Sixty-two aftershocks were located, evidence of the existence of a subfault(s). A secondary event(s) related to the subfault(s) is concluded to have caused the serious damage to the area around Baguio City.

Key words

great earthquake, earthquake fault, earthquake disaster, seismological observation, aftershock distribution