Introduction

The 16 July 1990 Luzon Earthquake and its Aftershock Activity

Soil Study of Area Damage due to Liquefaction during the 16 July 1990 Philippine Earthquake

Vital Engineering Lessons from the Earthquake of July 16, 1990

Quantifying Spatial and Temporal Dimensions of Premonitory Animal Behavior of the July 16, 1990 Luzon Earthquake

Households and Communities in a Post-Earthquake Situation: Lessons on Survival and Self-Reliance

Organizational Response to the July 1990 Luzon Earthquake Disaster

Psychosocial Issues in Disasters

Management Strategies for Earthquake-Related Psychosocial Problems Community-Based Interventions

Some Implications of the July 16, 1990 Earthquake on Urban and Regional Planning in the Philippines

The 16 July 1990 Luzon Earthquake and its Aftershock Activity
Bartolome C.Bautista, Ma. Leonila P.Bautista, Anel R. Rasdas
Angelito G. Lanuza, Erlinda Q. Amin and Perla J. Delos Reyes
Philippine Institute of Volcanology and Seismology - DOST

INTRODUCTION

The 16 July 1990 earthquake was the biggest earthquake too occur in the Philippines since 1976 and in Northern Luzon for the last century. Its negative impacts were so widespread and devastating that it brought to the fore the necessity to reassess and re-evaluate the effectivity of the existing disaster preparedness plans and programs of the government.

This study was sponsored by the Department of Environment and Natural Resources under the Documentation and Data Base Establishment of the July 16, 1990 Earthquake Program. For this particular study, we aim to achieve the following:

To present a summary of seismological information about the 16 July 1990 earthquake based on data from PHIVOLCS seismic network, and from short-term temporary seismic investigations by both PHIVOLCS and international groups of scientists.
Using seismological approaches, to explain why very extensive areas were devastated by the 16 July 1990 earthquake.
To present significant pre-earthquake observations which could be used as precursor for future earthquakes.

The Philippine Fault - the Culprit

The earthquake was triggered by the sudden movement of the northwest segment of Philippine Fault Zone (PFZ) and of its north trending splay, Digdig Fault. The PFZ is an active fault system which can be traced from Mindanao in south eastern Philippines, going north west and passing through the islands of Leyte, Masbate, Ticao Island, Bondoc Peninsula, Dingalan to Lingayen, Pangasinan (Figure 1). Based on geologic data, the age of the 1200-km long fault is estimated as Pliocene (Barrieret et.al., 1991). The latest pre-1990 movement of this fault occurred on, 17 March 1973 at Ragay Gulf in Quezon Province. That earthquake, with Ms of 7.5, resulted to horizontal displacements of 1.1 to 3.4 meters.

Along the rupture with no evident vertical component (Morante, 1974). From 1500 to 1983 at least 25 strong earthquakes (Figure 2) could be correlated to the movement of PFZ (Punongbayan and Umbal, 1990).

The most obvious geomorphological evidence of its recent movements could be found in Leyte in a series of offset streams and fault scarps. Other geomorphic features have been observed from field observations, satellite imagery, aerial photographs and seismic profiles (Barrier, et.al., 1991). According to Barrier et.al. (1991), there are two main segments the Philippine Fault - central section from Bondoc peninsula to Mindanao and the northern segment. The central segment is purely left-lateral strike-slip based on kinematic indicators while the northern segment has a thrust component.

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