The January 7 – 14 survey indicated Paleoseismic studies and Active Four major preliminary conclusions observation is that the epicenter of the 1990 was added to the 3 existing networks along the targeted activity for the program was to distinct anomalies in the total magnetic field Fault Mapping were made based on this year and the earthquake is located where shear stress the Philippine Fault in Central Philippines. generate a preliminary topographic map (TMF) along limited geothermal areas of previous years’ trenching activities. The first would be elevated by movements on the This network, comprising of 11 GPS and remote sensing imagery interpretation Daang Kastila and Main Crater Lake. In The objectives of this project are: (1) is thee identification evidence of four Gabaldon and San Jose faults. Preceding benchmarks installed in April 2005, covers of potential deposits at Leonard Volcano at February, permanent benchmarks were delineate the location of active faults and (2) surface-rupturing earthquakes along the earthquakes, most likely the 1645 an area of about 200 km x 100 km. The the scale of 1:50,000. constructed at the established magnetic to better understand the past activities of Digdig fault during the past 2000 years. The earthquake on the Gabaldon fault and the initial campaign was conducted in October observation points around Volcano Island. these faults through trenching. By trenching average recurrence interval of the fault is 1796 earthquake on the San Jose fault, may 2005. The establishment of this network was Out of the 22 active volcanoes in the Magnetic measurements confirmed areas of across the approximate trace of the fault, we about 600 years. The fault probably did not have controlled the location where the aimed at resolving the following questions: Philippines, very little is known about positive magnetic anomalies delineated by may be able to determine the number and rupture during the 1645 earthquake. rupture initiated in the 1990 earthquake. (1) Where does the NW extension of Leonard Volcano. The latest eruption of the January measurements. Positive timing of previous earthquakes, the repeat Additional samples are being dated to more Finally, it is possible that the recurrence Sibuyan Sea Fault terminate? (2) What is Leonard Volcano was 1,800 Bp. Based on anomalies were also observed in the periods between them, as well as the tightly constrain the timing of each events, interval of the individual segments of the extent of crustal deformation in the zone the photo-geologic interpretation done, there eastern part of the Main Crater Lake and on relative strength of these past events. especially the penultimate event. The Philippine fault zone is longer than 500 where the Philippine Fault and Legazpi is potential for an explosive eruption as the northern slope of Volcano Island (Daang second important findings is the fact that years, as we revealed for the Digdig fault, Lineament overlap? (3) What is slip rate of evidenced by the existence of ~2.8km Kastila). This was interpreted to be due to For this year, two separate trenching the San Jose fault ruptured at least three the occurrence of about ten M>7 the Philippine Fault in Ragay- Bondoc? diameter crater which generally implies that activation of the volcano’s hydrothermal activities were conducted across the Digdig times during the past 2500 years. The timing earthquakes during the past century may be (4)What is the relationship between the the latest eruption was very explosive. With system. Fault in Puncan, Nueva Ecija and along San of the most recent event is constrained interpreted as a temporal clustering of Philippine Fault and Sibuyan Sea Fault? the delineation of previous extent of Manuel Fault in San Manuel, Pangasinan sometime during the 15th and 19th century; activity for the fault zone. deposits through the photo-geologic map, The magnetic surveys made in January Fig. 6). the fault may have ruptured in 1796. Third Results that will be gathered from this we may be able to assess the possible and February was published as a Additional trenching activities will be network and that of the other networks can magnitude of past and future eruptions of proceeding of the workshop entitled conducted in early 2006 along Gabaldon be used eventually towards the the volcano. Following the photo-geologic “Magnetic and Electric Field Monitoring of Fault to complete the whole seismic history development of a comprehensive program map interpretation, delineation of hazards Taal Volcano, Philippines” Part 1: Magnetic of the Philippine fault in Northern Luzon. in evaluating seismic risks. will follow. Generated hazard map for Measurements, Japan Academy, Ser. B, This project is also being conducted in Leonard Volcano may be utilized for proper Vol. 81, No. 7, 2005. collaboration with Kyoto University. land use, disaster preparedness plans, and Kinematic analysis of Central Luzon Structures as guide for policy formulation. The The repeat survey conducted in August Ground deformation studies along photogeologic map was digitized using showed no significant deviation from the two the Philippine Fault For the year 2005, the following MapInfo to facilitate easy reproduction of the previous surveys. As of November, data map. activities were undertaken: (1) Interpretation gathered from the repeat magnetic survey is Although the Philippine Fault Zone of topographic maps complemented with still being processed. (PFZ) is recognized as the most active and interpretation of various imageries available Identification and characterization of destructive of the major earthquake such as Airsar and SAR, (2) Field mapping volcanic systems The EMSEV team of PHIVOLCS generators in the country, a number of its along the EZF in the Pangasina-Tarlac- constructed a vault for monitoring electric characteristics such as precise location, Pampanga area; (3) Documentation of Research areas and topics conducted field (self-potential) at the western side of segmentation, displacement rates and its morphotectonic features and gathering of under this project were the pyroclastic flow the upper Daang Kastila. The vault consists associated deformation, seismicity and wuantitative neotectonic and structural data deposits in Manila, 2000 pyroclastic flows of of PVC pipes and cable lines for continuous major earthquake recurrence are still along EZF and (4) trench site selection. Mayon Volcano and tephra deposits from measurement of SP and ground unknown. prehistoric and historic eruptions of Mayon temperature. Also established were several Out of these above-mentioned Volcano. thermal probe holes/observation points The objective of this project is to fill in activities, the following were produced: (1) along the Daang Kastila trail from the some of these missing information Active fault map of EZF from Airsar image The study on the upper Diliman tuff northern rim of the Main Crater down to the concerning the movement of the PFZ interpretation; (2) Active fault map of EZF used major and trace element bulk pumice basal slope of Volcano Island. through Global Positioning System (GPS) from SAR image interpretation; (3) Updated and mineral chemistry to interpret its origin monitoring. The use of GPS to study active 1:250, 000 strip map of EZF from topo map and evolution. This deposit is quite Taal Global Positioning System faults in our country is relatively new but its interpretation and field data; (4) Updated heterogeneous in terms of pumice potential to revolutionize PHIVOLCS’ 1:50,000 strip maps of EZF from topo map composition. Such heterogeneity can be The GPS monitoring network at Taal is earthquake prediction program is interpretation and field data and (5) Updated interpreted as mingling/mixing of partial a continuing collaborative project between considerable. GPS provides high-accuracy draft technical report incorporating results, melts produced by different degrees of VMEPD, Indiana University and UNAVCO. relative vector positioning that may be used interpretations, recommendations, maps, partial melting mostly within the crust. Initial There are 12 GPS stations on Taal Volcano in various tectonic studies such as and field data melting was still from the mantle and the Island and a master GPS station in determining plate motions to measuring slip chemistry shows the typical pattern for Tagaytay. This fruitful collaboration has rates of an individual fault zone. Through subduction zone magmas. The LILE values Geologic and hazard mapping of already generated one major research GPS measurements, complemented by active and potentially active for the upper Diliman are too high for publication on the magma dynamics and seismic data, fault segment which is volcanoes volcanoes along the volcanic front (Bataan ground deformation published last October accumulating strain may be identified, and Arc) and are more similar to Laguna in the Journal of Geophysical Research. hence the probable site of the next probable The main goal of the program is to deposits. In terms of other elements earthquake may be located. identify potential volcanic hazards and however, results indicate that the upper generate volcano-geologic maps not only for Diliman tuff is chemically distinct from Taal For this year another GPS network, the and Laguna Caldera pyroclastic flow active volcanoes in the Philippines but also Fig. 6. Trench site along the Digdig Fault in Puncan, Caranglan, Nueva Ecija (Paleoseismology and Active Faults Ragay-Bondoc network in Southern Luzon, deposits. They cannot be related by for potentially active volcanoes. For 2005, Mapping Project) 12 13 fractional crystallization, and there are stratigraphy and clear-cut aggradational tephra units. Ultimately, the tephrochrono- differences in the degrees of partial melting emplacement; and massive framework logy will be used to establish the eruptive for each source, which may or may not agglutinate bomb-rich units which are in history of Mayon Volcano. RR&&DD pprroo ggrraammss aanndd oo tthheerr reflect across arc variation. themselves new evidence of direct emanation from the colder, outer parts of the Study of tectonic uplift and CCoollllaabboo rraattiivvee PPrroojjee ccttss The study on the 2000 pyroclastic flows lava fountains.