Tectonic Controls on Magmatism at Taal Volcano, Philippines

Space geodetic methods combined with imaging are used to inspect active tectonics and magmatism within the Macolod Corridor and the Taal Caldera, a geologically complex area in Southwestern Luzon. This area is characterized by extensive volcanism and widespread faulting. Radar and multispectral imageries subjected through analytical shading and image filtering techniques and combined with digital terrain models are used to analyze fault orientations and detailed geomorphic features of the area. Campaign geodetic observations (1996-2002) from GPS stations within Luzon are used in combination with remote sensing and earthquake slip vectors to derive the kinematics of Luzon. We use an elastic block modeling approach, which characterizes crustal deformation as a result of rotation of discrete elastic microplates around Euler poles. The resulting best-fit model indicates that the Luzon area is composed of six microplates. The vicinity Macolod area in SW Luzon is best represented with three mobile microplates. Active tectonics of the Philippine mobile belt is dominated by eastward subduction along the Manila Trench (~20-100 mm y-1), westward subduction along the Philippine Trench (~29-34 mm y-1), and sinistral strike-slip faulting along the Philippine Fault (~10-40 mm y-1). The velocity field indicates localized transpression along the N-S trending Marikina Fault (~10-12 mm y-1), and transtensional motion along the NE-SW trending Macolod Corridor fault zone (~5-10 mm y-1). Observations from the continuous single- and dual-frequency GPS stations of the Taal Volcano network from 1998-2005 indicate a sequence of inflationary and deflationary events, which include several periods of rapid volcanic inflation (~120 mm uplift from February to November 2000) and rapid deflation (~33 mm subsidence from June to December 1999). The most recent episode of inflation extended from June 2004 to March 2005 indicated ~73 mm y-1 extension across the volcanic edifice, with about 50 mm uplift with respect to the caldera wall. A recent deflationary pattern starting April 2005 is also detected. Models for the earlier inflation and deflation events indicate that a Mogi point source 4-5 km deep centered at the Volcano Island describes the deformation effectively. The inflationary trends are interpreted to be episodes of magma intrusion to a shallow reservoir beneath Volcano Island, which is significantly affected by regional tectonism.