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，我们还调查了2003年5月开始喷发的阿纳塔罕岛的火山活动，这在人类历史上是第一次。GPS观测是在2003年1月、2003年7月和2004年5-6月进行的。对获得的数据进行了分析，同时考虑了较早的数据。考虑到最北端的三个岛屿只被观测过一次，我们在这三个岛屿，即阿森西翁、毛格岛和乌拉库斯岛进行了广泛的观测。结果表明，马里亚纳海槽的弧后扩张效应在该地区十分明显。然而，在北部的三个岛屿，表明弧后扩张影响的残差向量显示出一些不同的向量。弧后扩张的效果不是很明显。这可能是因为只有一年的观测时间所致。我们应该做更详细的分析…更多的数据。此外，未来我们可能不得不重复GPS观测，以获得更可靠的结果。阿纳塔罕火山于2003年5-6月开始喷发。5月10日晚，安山岩岩浆在峰顶火山口东部的东部火山口开始了一系列次大陆爆发性喷发。布朗·特弗拉主要由强风向西移动。5月下旬，小规模的火山碎屑涌流向东排出了火山口。6月中旬，安山岩熔岩穹顶曾经填满了内部陨石坑，现在却被火山喷发的火山灰碎裂了。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而发生的，火山口内和岛上大部分地区都有大量的非常细的火山灰(“灰色火山灰”)排出。5-6月喷发产物的体积估计为1.4×10~(-7)m~(-3)致密岩当量。喷发的浮石和熔岩是硬安山岩，根据其泡孔程度不同，颜色也不同。喷发物中的SiO_2含量随时间略有下降。细灰中的碱性物质被耗尽，这可能是由于爆炸过程中酸性热液的淋溶作用。2004年3月下旬恢复了地震活动，2004年5月和6月又发生了类似于闪电爆炸的小规模爆炸。内部陨石坑的大约坚硬部分充满了新的火山灰和熔岩。较少

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