Research for the Volcanic and Seismic Activity in Luzon

1)吕宋岛西南部的Macolod走廊是一个宽约40 km的活跃的第四纪强烈火山活动带，沿NE-SW方向垂直于该岛，该带被认为是一个拉分裂谷带。为了确定Macolod走廊地壳运动的位移速度，进行了GPS测量。在1996年4月和9月的观测期间，在吕宋岛、民都洛岛和马林杜克岛建立了13个监测站。每站24小时连续测量3-6天，测量速率为每30秒一个样品。在对马尼拉IGS站的数据进行基线分析后，我们得到了Macolod走廊及其周围的位移速度，显示出2 cm/年的大值。为了检验这个数值是否包含了大气水汽造成的误差，我们于1997年1月和2月在9个站点进行了5天的GPS观测。2)为了检查马尼拉和内格罗海沟之间是否存在板块，我们在吕宋岛、民都洛岛、马induque岛、Tablas岛、西布延岛和班乃岛设置了9个地震台站，并监测了该地区的地震活动。车站之间的距离从60公里到90公里不等。然而，在9个月的观测期间，由于观测周期短、地震活动性低，再加上停电等技术问题，我们只对部分台站周围的局部地震活动进行了定向，无法沿俯冲板获得震源。3)为了研究Macolod走廊破火山口前喷发物质和岩浆管道系统的历史，我们采集了大型破火山口火山Taal火山和Lagna de Bay周围的火山岩样品。开展了微量元素分析、K-Ar定年等岩石学和年代学研究。

1) The Macolod Corridor in Southwestern Luzon is an approximately 40 km wide zone of active intense Quaternary volcanism which crosses perpendicular the Island in a NE-SW direction and this zone is considered to be a pull-apart rift zone. In order to determine the displacement velocity of crustal movement in Macolod Corridor, GPS measurements were executed. Thirteen stations were established in Luzon, Mindoro, and Marinduque islands during observation period in April and September, 1996. A 24 hours continuous measurement was made for 3-6 days at each station with a rate of one sample per 30 seconds. After a baseline analysis including data at Manila, IGS station, we got a displacement velocity in and around the Macolod Corridor, which shows such a large value as 2 cm/year. To check whether this value includes some errors caused by vapor in atmosphere, we executed a GPS measurement at 9 stations in January and February, 1997 with a observation period of 5 days.2) To check the presence of a slab between the Manila and the Negros trenches, we installed 9 seismic stations in Luzon, Mindoro, Marinduque, Tablas, Sibuyan and Panay islands and seismic activity in this region was monitored. Distances between stations varied from 60 to 90 km. However, during the nine-month observation period, only local seismicity around some stations were directed and we could not get a hypocenter along a subducting slab because of short period observation, low seismicity, and some technical problems like power failure.3) In order to study pre-calderagenic eruption material and history of magma plumbing system in the Macolod Corridor, we collected volcanic rock samples around Taal volcano, a large caldera volcano, and Lagna de Bay. Petrological and Geochronological study were started such as trace element analysis and K-Ar dating.