[S12-P] Poster

[S12-P-03] Resistivity changes during the 2015 seismic swarm detected by real-time magnetotelluric monitoring system in Taal volcano (Philippines)

^○Paul Karson Alanis¹, Paolo Reniva¹, Juan Cordon¹, Allan Loza¹, Lawrence Aaron Banes¹, Yoichi Sasai², Akihiro Takeuchi³, Toshiyasu Nagao² (1.Philippine Institute of Volcanology and Seismology, 2.Institute of Oceanic Research Development, Tokai University, Japan, 3.Earthquake Research Institute, The University of Tokyo, Japan)

Taal volcano is located in the island of Luzon and 60 km south of the capital city of Manila. It is one of the most active volcanoes in the Philippines. The first recorded eruption was in 1573 and since then it has erupted a total of 33 times, with the last eruption in 1977. These eruptions resulted in thousands of casualties and considerable damage to property. In 1995 it was declared one of the “1990s decade volcano" by IAVCEI. Although the volcano remained fairly quiescent after the 1977 eruption, at the beginning of the 1990s it began to exhibit several phases of abnormal activities, such as episodes of seismic swarms, ground deformation and fissuring, and hydrothermal activities, all of which continues to the present. Past eruptions of Taal Volcano can be divided into 2 distinct cycles, depending on the location of the eruption: eruptions centered at the Main Crater (1572-1645 and 1749-1911); and eruptions occurring at the flanks (1707-1731; 1965-1977).
As part of the PHIVOLCS-JICA-SATREPS Project (2010-2014), magnetometers were installed at Taal volcano. These consist of three (3) Overhauser-type magnetometers (installed at VTBM, VTDK and VTMC) and one (1) fluxgate-type magnetometer (installed at VTBM). The Project also established (using magentotelluric method) that a large hydrothermal reservoir is underneath Taal volcano and currently this is under a state of equilibrium. The state of the hydrothermal reservoir is thus monitored constantly by magnetometers. In early-2015, remarkable resistivity changes were detected by the flux-gate magnetometer during an earthquake swarm occurred in Taal volcano. The locations of these earthquakes appears to be in the approximate location of the hydrothermal reservoir.