Analysis of GPS Measurement in West-Java, Indonesia

Abstract

インドネシアのジャワ島西部では、1992年以来日本との共同研究として数回のGPS観測を行ってきた。ジャワ島の南でインド・オーストラリアプレートがユーラシアプレート下へ沈み込むためこ生じる運動を反映しているものと解釈されているCimandiriおよびLembang両断層の現在の運動を調べるため、14点からなる観測網を設置した。1996年12月の観測における平均二乗誤差は0.4-3.5mmとなり、南北成分は東西成分に比べ1.5倍、また上下成分は約3倍悪い。以前の観測と比較した結果は、インド・オーストラリアプレートの沈み込みによる変形と調和している。Cimandiri断層の北側は北東方向への動きを示唆しており、南側は圧縮の傾向をしめしている。

GPS Measurements for geodynamics study in West-Java, Indonesia, have been done several times, since 1992 by a cooperating group between Japan and Indonesia. For these measurements, 14 pillars have been settled to cover, for the first time, two geological structures, the Cimandiri and Lembang fault zones. These phenomena are assumed as one of the compensation of subduction process of Indo-Australian plate beneath the Eurasian plate in the south of Java Island, which has a velocity of 71 mm/yr at 20°azimuth relative to the Eurasian plate (NUVEL- 1).The December 1996 campaign gave a result with an rms error error between 0.4 and 3.5 mm, when one coordinate at ITB1 was kept fixed. The N-S components give rms error around 1.5 times better than the E-W and the height component, as expected, give three times larger than the horizontal components.Comparing to previous campaigns, the 1996 campaign shows a trend of deformation vectors which are in agreement to the global model of plate tectonics. The northern part of the Cimandiri fault zone moved to the northeast direction, relative to ITB1 Station, which is laid in the southern part. The calculated strain from GPS result also shows that there is a compression process within the area in NE-SW direction