馬榮火山(Mayon Volcano) 是一座位於菲律賓呂宋島的東南端，高2463公尺且對稱錐形複式安山岩火山(Stratovolcano)。它屬於位在菲律賓斷層中段的Bicol火山鏈，為世界最活躍火山之一。馬榮火山爆發歷史紀錄始於西元1616年，至今總共噴發了50次。馬榮火山近年的爆發紀錄共有四次，分別在2004年7月、2005年8月、2006年2月及7月。利用高精度全球定位系統(GPS)連續觀測站可監測地殼變形的活動，為火山研究提供參考作用。本研究之資料由菲律賓火山地震研究所(PHIVOLCS)所提供，採用2004年至2006年馬榮火山附近七個GPS站的每日觀測數據，同時匯集了全球導航衛星系統國際服務IGS (International GNSS Service) 的數據，應用GAMIT/GLOBK 軟件進行整體分析。以國際地球參考框架ITRF2005 對每觀測站進行點位座標、水平及垂直速度場分析。利用解算後所得之座標時間序列及基線長度變化，可將馬榮火山隨時間變化的變形形態區分為二個階段：一、火山體積膨脹階段，分別發生在2004年1月至10月、2005年2月至8月、與2006年1月至8月；二、火山體積收縮階段，分別發生在2004年11月至2005年1月、與2005年9月至12月。馬榮火山爆發前，岩漿庫能量持續累積，使得地表變形以火山口為中心呈現膨脹形態，造成火山週遭GPS測站基線長度相對增加，於2005年8月測站基線長度增長量最大值為2.1cm。在火山爆發期間，座標時間序列呈快速膨脹收縮且離散度大，於2006年7月時水平方向離散程度最大為2.4cm，高程方向最大為6.7cm。火山爆發後，活動行為不呈現全向火山口收縮狀態，受區域構造影響大(Lagaspi L Fault 左移斷層－西北走向)。而每次火山爆發事件前皆有地表膨脹變形，能量累積時間和噴發事件大小無相關性。利用Mogi model套用於2005年火山爆發後GPS測站位移變化，得知位於火山口南邊測站，活動行為較單純，觀測值和計算值一致；北邊測站受Lagaspi L Fault左移分量、測站位置等因素影響，故計算值和觀測值相異大，而model計算之misfit值為2.278公分。由於馬榮火山具有高度活動行為，火山位置和人類居住地相近，了解馬榮火山且將危害降低是重要議題。

Mayon Volcano, which is located in the Bicol Basin in the southeastern region of Luzon, Philippines, is a nearly symmetric stratovolcano with an elevation of 2463 m above the plains of the Bicol Basin. The central segment of the Philippine Fault near the Bicol region is a releasing bend. It has erupted 50 times since the first recorded eruption in 1616 and is the most active volcano in Philippines. During 2004-2006, the eruptions occurred on July 2004, August 2005, February 2006, and July 2006, respectively. Continuous Global Positioning System (GPS) stations are useful in investigating crustal deformations. To monitor the movement of Mayon volcano, PHIVOLCS setup 7 continuous GPS stations around the Mayon volcano in late 2003. In this study, we analyzed the daily observational data collected at Mayon volcano from January 2004 to November 2006 in conjunction with the global GPS data from International GNSS Service using the GAMIT/GLOBK software package. Calculated point-position coordinates are referred to the International Reference framework (ITRF2005). Using the coordinates time series and changes in baseline length, deformation patterns between 2004 and 2006 are divided into two stages at Mayon volcano: First, the volcanic volume expansion occurred, respectively from January to October in 2004, from February to August in 2005 and from January to August 2006; Second, volcanic volume contraction phase occurred, respectively from November 2004 to January 2005, and from September to December in 2005. Before volcanic eruption, the magma chamber with accumulating magma caused inflation at the crater. The relative baseline shows change over the entire observation period. Baseline analysis between network sites shows that baseline with a maximum is up to 2.1 cm in August 2005. During volcanic eruption, GPS time series shows more outliers, and the rapid inflation and deflation. The maximum horizontal displacement is 2.4 cm and the maximum vertical displacement is 6.7 cm in July 2006. After volcanic eruption, most of deformations observed on the regional GPS sites are therefore belonging to inflation at the crater but reflect regional tectonics that have been recognized as part of Lagaspi L Fault, which is a left-lateral strike-slip fault. Moreover, some of excursions on Mayon volcano deformation time series show no correlation with duration of magma storage and the levels of eruptions. Even though, the ground deformation reflects an overall inflation. By applying Mogi model to the event on 2005, we find that the variation of displacement observed by GPS stations. The behaviors indicate that the observed values are not significantly different from calculated values in the southern sites. However, it shows no correspondence in the northern sites between observations and calculations due to regional tectonics. The misfit value of model calculations is 2.278 cm. These results obtained so far indicate that the deformations are cased by volcanic edifice, regional surroundings as well as GPS sites location. Because of the frequent activities of Mayon and the growing populations around the volcano, it is necessary to understand the activities of Mayon volcano and it is also an important issue about how to prevent hazards from volcanic eruption.

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