Research on the tectonics of the southeastern Philippine Sea based on GPS observations

我们对北马里亚纳群岛、北马里亚纳群岛联邦的构造运动进行了重复的GPS观测。此外，我们还对2003年5月人类历史上首次喷发的Anatahan岛的火山活动进行了调查。GPS观测分别于2003年1月、2003年7月和2004年5 - 6月进行。对获得的数据进行了分析，并考虑了先前的数据。考虑到最北端的三个岛屿没有被观察过一次以上，我们在这三个岛屿，即阿森西翁、莫格和乌拉库斯岛进行了广泛的观察。结果表明，该地区马里亚纳海槽弧后扩张作用明显。然而，在北部三个岛屿，表明弧后扩散影响的剩余矢量显示出一些发散的矢量。弧后扩散的影响不是很明显。这可能是由于观测时间很短，只有一年。我们应该做更详细的分析…更多的数据。此外，为了获得更可靠的结果，我们可能需要在未来重复GPS观测。2003年5月至6月，安纳塔汉火山开始喷发。5月10日晚，在峰顶破火山口东部的东部火山口开始了一系列安山岩岩浆的次喷发。Brown tephra主要被强风吹向西部。5月下旬，小规模的火山碎屑涌向东排出火山口外。一个安山岩熔岩穹窿曾经填满了内部的火山口，在6月中旬的火山喷发中破碎了。火山喷发可能是由于岩浆铅与火山口周围的地下水相互作用造成的，大量极细的火山灰（“灰色火山灰”）在火山口内和岛上大部分地区被释放出来。估计5 - 6月喷发产物的体积为1.4 × 10^7 m^3致密岩当量。喷发出来的浮石和熔岩是无色安山岩，根据它们的泡状而呈现出不同的颜色。随着时间的延长，喷发物的SiO2含量略有下降。细灰在碱中被耗尽，可能是由于爆炸期间酸性热液的浸出。2004年3月下旬，地震活动恢复，2004年5月和6月又发生了类似飓风的小型爆炸。大约有一半的内火山口充满了新的火山渣和熔岩。少

We have repeated GPS observations for darifying tectonic motion in the Northern Mariana Islands, Commonwealth of the Northern Mariana Islands. Moreover, we investigated the volcanic activity of Anatahan Island that began eruption in May 2003 for the first time in the human history. GPS observations were conducted in January 2003, July 2003 and May-Jun 2004. The obtained data were analyzed taking earlier data into consideration. Considering that the northernmost three islands were not been observed more than once, we extensively made observations in those three islands, namely, Asencion, Maug and Uracus. Results show that the effect of back-arc spreading in the Mariana Trough is eminent in the region. However, at the northern three islands, residual vectors that indicate effects of back-arc spreading show somewhat diverging vectors. The effect of back-arc spreading is not very eminent. This is probably due to short observation time of only one year. We should make more detailed analysis … More of the data. In addition, we may have to repeat GPS observations in the future to obtain more reliable results.Anatahan volcano began erupting in May-Jun 2003. A series of subplinian explosive eruptions of andesite magma began at the Eastern Crater in the eastern part of the summit caldera on the evening of 10 May. Brown tephra was sent mainly westward by strong winds. Small-scale pyroclastic surges were discharged eastward outside the caldera in late May. An andesite lava dome that had once filled the inner crater was fragmented by phreatomagmatic explosions in the middle of June. The phreatomagmatic explosions probably occurred due to interaction of the magma lead with ground water around the crater, and abundant very fine ash ("gray tephra") was discharged within the caldera and over most of the island. The volume of eruption products of the May-June eruption was estimated to be 1.4x10^7 m^3 dense-rock-equivalent. Erupted pumices and lava are aphyric andesite and are variously colored depending on their vesicularity. The SiO2 contents of erupted materials decreased slightly with time. The fine gray ash is depleted in alkalies, probably due to leaching by acid hydrothermal fluids during explosions. Seismic activity resumed in late March 2004, and small strombolian-like explosions were repeated in May and June 2004. About hard of the inner crater was filled with new scoria and lava. Less