Glenda Besana - Academia.edu (original) (raw)
Papers by Glenda Besana
The Tsunami Society publishes this journal to increase and disseminate knowledge about tsunamis a... more The Tsunami Society publishes this journal to increase and disseminate knowledge about tsunamis and their hazards. DISCLAIMER: Although these articles have been technically reviewed by peers, The Tsunami Society is not responsible for the veracity of any statement, opinion or consequences.
Earth, Planets and Space, 2005
The central Philippine Fault Zone is found to be the locus of great earthquakes, a transition zon... more The central Philippine Fault Zone is found to be the locus of great earthquakes, a transition zone with slow slip and creep activity. This is based on the analysis and correlation of seismic historic data and detailed documentation of recent seismic events in the region. Based on this study the Guinyangan fault is defined to be the northern locked portion with recurrence interval of as short as 65 years. The Masbate fault is the central part with large and medium earthquakes accompanied by unusually large ground rupture. The north Central Leyte fault and the south Central Leyte fault, on the other hand, are characterized by aseismic creep and medium-sized events, usually with clusters of foreshocks, respectively. Unusual seismic activity both on the Masbate fault and Central Leyte fault somehow correlates well with the behavior of known slow events and creep activity. Further investigation of this region could lead to deeper understanding of impending major earthquakes, especially a...
Bulletin of the Seismological Society of America, 2014
In probabilistic seismic-hazard analysis (PSHA), seismic source zone (SSZ) models are widely used... more In probabilistic seismic-hazard analysis (PSHA), seismic source zone (SSZ) models are widely used to account for the contribution to the hazard from earthquakes not directly correlated with geological structures. Notwithstanding the impact of SSZ models in PSHA, the theoretical framework underlying SSZ models and the criteria used to delineate the SSZs are seldom explicitly stated and suitably documented. In this paper, we propose a methodological framework to develop and document SSZ models, which includes (1) an assessment of the appropriate scale and degree of stationarity, (2) an assessment of seismicity catalog completeness-related issues, and (3) an evaluation and credibility ranking of physical criteria used to delineate the boundaries of the SSZs. We also emphasize the need for SSZ models to be supported by a comprehensive set of metadata documenting both the unique characteristics of each SSZ and the criteria used to delineate its boundaries. This procedure ensures that the uncertainties in the model can be properly addressed in the PSHA and that the model can be easily updated whenever new data are available. The proposed methodology is illustrated using the SSZ model developed for the Azores-West Iberian region in the context of the Seismic Hazard Harmonization in Europe project (project SHARE) and some of the most relevant SSZs are discussed in detail. Online Material: Tables describing characteristics and boundaries of the seismic source zones.
Journal of Geophysical Research, 2008
We developed a new geodetic method of monitoring crustal deformation on the ocean floor. The meas... more We developed a new geodetic method of monitoring crustal deformation on the ocean floor. The measurements were conducted at two sites beneath the Pacific Ocean, near the Nankai Trough, where the Philippine Sea plate subducts into the Pacific plate. The first site was at a depth of 700 m in Suruga Bay, and the second one was at a depth of 2000 m in the Kumano Basin. At each survey site, three seafloor transponders, whose positions were repetitively measured, were deployed to define a benchmark unit. An ultrasonic signal was generated from a surface vessel drifting over the benchmark unit that was transmitting and receiving the signal and the replies from the transponders. Both sound speed structure and the benchmark unit positions were determined simultaneously using a tomographic technique. We repeatedly carried out measurements over the two sites. For the Kumano Basin we made six measurements from July 2004 to August 2005. The benchmark unit location's horizontal precision was 5 cm, and its vertical precision was 10 cm. For Suruga Bay we made five measurements, and the positions were less accurate, with horizontal variation of 7 cm and vertical variation of 16 cm. We investigated the reason for the decreased precision in Suruga Bay with a numerical experiment, and the results revealed that the geometry of the measurement, that is, the vessel's path, is one of the most important variables in our method. At the Kumano Basin a 21.5-cm southward displacement of the benchmark unit was detected just below the site before and after a large earthquake (Mw 7.5). Our observation system therefore proved itself capable of detecting seafloor crustal deformation associated with crustal activities in offshore areas.
Science of Tsunami …, 2004
... Hannah Mirabueno 2Philippine Institute of Volcanology & Seismology, Department of... more ... Hannah Mirabueno 2Philippine Institute of Volcanology & Seismology, Department of Science and Technology, Quezon City, Philippines 1104 ... interviewees both through a patterned set of questions and through their own spontaneous accounts from the time they felt the strong ...
Geophysical Research Letters, 2006
We have developed an observation system for seafloor crustal deformation measurement combining th... more We have developed an observation system for seafloor crustal deformation measurement combining the two following techniques: the precise acoustic ranging and kinematic GPS (Global Positioning System) positioning. On July 14, 2003, we installed the units for this observation system at the seafloor of the Kumano Basin, Japan (33.58°N, 136.60°E). We performed repeated observation six times on 1
Earth and Planetary Science Letters, 1997
Attenuation structures were determined for the Philippine archipelago by inversion of earthquake ... more Attenuation structures were determined for the Philippine archipelago by inversion of earthquake intensity data set from 1957 to 1992. The intensity data based on the Adapted Rossi-Fore1 Intensity Scale were translated into acceleration values using a modified acceleration-intensity equation. A damped least-squares method was used in our inversion. We correlated the inversion results with other data, such as observed anomalous intensity distribution, present seismicity, and the location of trenches and volcanic centers. Our results strongly indicate the association of low attenuation values with subducted slabs along the known location of trenches in the Philippines. For example, the configuration of the Philippine Trench is suggested by the concentration of low attenuation values along the east side of central and southern Philippines while on the western side of Luzon Island a low attenuation structure is consistent with the location of the Manila Trench. The extent and depth of low attenuation values are also apparent along the eastern side of Luzon. In southern Luzon through Negros Island in the central Philippines, the site where anomalous intensity distribution was observed coincided with the location of a noticeable low-attenuation structure determined in this study. Moreover, possible locations of an upwelling magmatic body along the numerous areas in the Philippines are also indicated by the concentration of high attenuation values. Furthermore, a possible aseismic slab, which probably represents a structure that connects the Manila Trench with the Negros Trench, was also inferred in Eastern Mindoro. However, it is also possible that these low attenuating values are due to the presence of continental material in this area. On the basis of these initial results, we suggest some modifications of the configuration of tectonic structures in several portions of the archipelago.
Geophysical Research Letters, 1995
Depths of the partially melted zone and the Moho discontinuity are probably at 18 kilometers and ... more Depths of the partially melted zone and the Moho discontinuity are probably at 18 kilometers and 34 kilometers, respectively beneath Tagaytay seismic station, Luzon, Philippines. This conclusion is based on the shear-wave velocity structure determined in this study, which indicates the presence of a low-velocity zone and high-velocity zone at these depths. The shear wave velocity model was derived from the inversion of five receiver functions of teleseismic earthquakes recorded by the broadband seismometer at Tagaytay. However, due to the very limited information to constrain our initial model, other models with comparable waveform fit were also obtained but with deeper low velocity zone and shallower Moho. introduction in this paper, we use the data recorded by a broadband Streckheisen (STS-2) seismometer in Tagaytay seismic station (Besanaetal., 1993; Fukao, 1991). Tagaytay station (TGY)is located about 10 km north of the Taal Volcano island and sits along the outer ridge of Taal caldera, Batangas in southern Luzon (Figure 1). To the east of the study area is the westwardsubducting Philippine Sea Plate and the Philippine Fault Zone (PFZ), while to the west is the eastward-vergent Manila Trench subduction zone. Forster et al. (1990) suggested that the volcanoes in the area belong to the Macolod Corridor, a structure thought to be a rift zone between the Manila Trench and the PFZ (Defant et al., 1988) or probably formed from crustal thinning and/or complex partial melting beneath Batangas area (Besana, 1995). Major structures that traverse the area include the northern Sibuyan Sea branch of the PFZ (Bischke et al., 1990) and the southern extension of the West Marikina Valley Fault (Daligdig et al., 1993; Wolfe and Self, 1983). Listanco (1994) analyzed the petrochemical characteristics of basalts at Taal Volcano and distinguished two basalt groups with distinct mineral assemblages and corresponding depths of crystallization/generation. The more dominant basalt group has an olivine-clinopyroxeneplagioclase assemblage that suggests a depth of crystalization of not more than 5 kb which is roughly 15-20 km deep while the minor rock group shows near-primary magma characteristics (high MgO, Ni, and low FeO/MgO) possibly generated at about 10-11 kb. Based on the presence of later phases and attenuated spectral amplitude of signals passing beneath the northeastern portion of Taal Volcano, the existence of reflectors at depths of 1 and 8 km in Taal was determined by Nishigami et al. (1994) using the fan-shooting Copyright 1995 by the American Geophysical Union. Paper number 95GL03319 0094-8534/95/95GL-03319503.00 technique. Other studies conducted in the area largely dealt on the geology and activity of Taal Volcano (Alcaraz and Datuin, 1974; Geronimo, 1988; Knittel and Defant• 1988; Torres et al., 1990). Therefore, the structure of the crust and uppermost mantle beneath TGY is almost unknown.
Resource Geology, 2005
ABSTRACT High seismic activity in the Philippines originates from tectonic convergence related to... more ABSTRACT High seismic activity in the Philippines originates from tectonic convergence related to surface and subsurface seismotectonic features. Based on earthquake data, the archipelago can be divided into the seismically-active Philippine Mobile Belt and the aseismic North Palawan Block. The latter represents a rifted continental fragment of the Eurasian margin that juxtaposed with the rest of island arc units in central Philippines. Earthquake hypocenter plots on planar and in vertical profiles show that the seismic events are associated with known seismotectonic features. In addition, data suggest that the collision zone between the North Palawan Block and the Philippine Mobile Belt is characterized by a decreased amount of hypocenters at > 100 km depths. Although field evidence favors the presence of a subducted slab or slabs beneath western central Philippines, these are difficult to image using the present seismicity distribution dataset.
Geophysical Research Letters, 2006
We have developed an observation system for seafloor crustal deformation measurement combining th... more We have developed an observation system for seafloor crustal deformation measurement combining the two following techniques: the precise acoustic ranging and kinematic GPS (Global Positioning System) positioning. On July 14, 2003, we installed the units for this observation system at the seafloor of the Kumano Basin, Japan (33.58°N, 136.60°E). We performed repeated observation six times on 1) July 15–16 and
Journal of Geophysical Research, 2008
We developed a new geodetic method of monitoring crustal deformation on the ocean floor. The meas... more We developed a new geodetic method of monitoring crustal deformation on the ocean floor. The measurements were conducted at two sites beneath the Pacific Ocean, near the Nankai Trough, where the Philippine Sea plate subducts into the Pacific plate. The first site was at a depth of 700 m in Suruga Bay, and the second one was at a depth of 2000 m in the Kumano Basin. At each survey site, three seafloor transponders, whose positions were repetitively measured, were deployed to define a benchmark unit. An ultrasonic signal was generated from a surface vessel drifting over the benchmark unit that was transmitting and receiving the signal and the replies from the transponders. Both sound speed structure and the benchmark unit positions were determined simultaneously using a tomographic technique. We repeatedly carried out measurements over the two sites. For the Kumano Basin we made six measurements from July 2004 to August 2005. The benchmark unit location's horizontal precision was 5 cm, and its vertical precision was 10 cm. For Suruga Bay we made five measurements, and the positions were less accurate, with horizontal variation of 7 cm and vertical variation of 16 cm. We investigated the reason for the decreased precision in Suruga Bay with a numerical experiment, and the results revealed that the geometry of the measurement, that is, the vessel's path, is one of the most important variables in our method. At the Kumano Basin a 21.5-cm southward displacement of the benchmark unit was detected just below the site before and after a large earthquake (Mw 7.5). Our observation system therefore proved itself capable of detecting seafloor crustal deformation associated with crustal activities in offshore areas.
The Tsunami Society publishes this journal to increase and disseminate knowledge about tsunamis a... more The Tsunami Society publishes this journal to increase and disseminate knowledge about tsunamis and their hazards. DISCLAIMER: Although these articles have been technically reviewed by peers, The Tsunami Society is not responsible for the veracity of any statement, opinion or consequences.
Earth, Planets and Space, 2005
The central Philippine Fault Zone is found to be the locus of great earthquakes, a transition zon... more The central Philippine Fault Zone is found to be the locus of great earthquakes, a transition zone with slow slip and creep activity. This is based on the analysis and correlation of seismic historic data and detailed documentation of recent seismic events in the region. Based on this study the Guinyangan fault is defined to be the northern locked portion with recurrence interval of as short as 65 years. The Masbate fault is the central part with large and medium earthquakes accompanied by unusually large ground rupture. The north Central Leyte fault and the south Central Leyte fault, on the other hand, are characterized by aseismic creep and medium-sized events, usually with clusters of foreshocks, respectively. Unusual seismic activity both on the Masbate fault and Central Leyte fault somehow correlates well with the behavior of known slow events and creep activity. Further investigation of this region could lead to deeper understanding of impending major earthquakes, especially a...
Bulletin of the Seismological Society of America, 2014
In probabilistic seismic-hazard analysis (PSHA), seismic source zone (SSZ) models are widely used... more In probabilistic seismic-hazard analysis (PSHA), seismic source zone (SSZ) models are widely used to account for the contribution to the hazard from earthquakes not directly correlated with geological structures. Notwithstanding the impact of SSZ models in PSHA, the theoretical framework underlying SSZ models and the criteria used to delineate the SSZs are seldom explicitly stated and suitably documented. In this paper, we propose a methodological framework to develop and document SSZ models, which includes (1) an assessment of the appropriate scale and degree of stationarity, (2) an assessment of seismicity catalog completeness-related issues, and (3) an evaluation and credibility ranking of physical criteria used to delineate the boundaries of the SSZs. We also emphasize the need for SSZ models to be supported by a comprehensive set of metadata documenting both the unique characteristics of each SSZ and the criteria used to delineate its boundaries. This procedure ensures that the uncertainties in the model can be properly addressed in the PSHA and that the model can be easily updated whenever new data are available. The proposed methodology is illustrated using the SSZ model developed for the Azores-West Iberian region in the context of the Seismic Hazard Harmonization in Europe project (project SHARE) and some of the most relevant SSZs are discussed in detail. Online Material: Tables describing characteristics and boundaries of the seismic source zones.
Journal of Geophysical Research, 2008
We developed a new geodetic method of monitoring crustal deformation on the ocean floor. The meas... more We developed a new geodetic method of monitoring crustal deformation on the ocean floor. The measurements were conducted at two sites beneath the Pacific Ocean, near the Nankai Trough, where the Philippine Sea plate subducts into the Pacific plate. The first site was at a depth of 700 m in Suruga Bay, and the second one was at a depth of 2000 m in the Kumano Basin. At each survey site, three seafloor transponders, whose positions were repetitively measured, were deployed to define a benchmark unit. An ultrasonic signal was generated from a surface vessel drifting over the benchmark unit that was transmitting and receiving the signal and the replies from the transponders. Both sound speed structure and the benchmark unit positions were determined simultaneously using a tomographic technique. We repeatedly carried out measurements over the two sites. For the Kumano Basin we made six measurements from July 2004 to August 2005. The benchmark unit location's horizontal precision was 5 cm, and its vertical precision was 10 cm. For Suruga Bay we made five measurements, and the positions were less accurate, with horizontal variation of 7 cm and vertical variation of 16 cm. We investigated the reason for the decreased precision in Suruga Bay with a numerical experiment, and the results revealed that the geometry of the measurement, that is, the vessel's path, is one of the most important variables in our method. At the Kumano Basin a 21.5-cm southward displacement of the benchmark unit was detected just below the site before and after a large earthquake (Mw 7.5). Our observation system therefore proved itself capable of detecting seafloor crustal deformation associated with crustal activities in offshore areas.
Science of Tsunami …, 2004
... Hannah Mirabueno 2Philippine Institute of Volcanology & Seismology, Department of... more ... Hannah Mirabueno 2Philippine Institute of Volcanology & Seismology, Department of Science and Technology, Quezon City, Philippines 1104 ... interviewees both through a patterned set of questions and through their own spontaneous accounts from the time they felt the strong ...
Geophysical Research Letters, 2006
We have developed an observation system for seafloor crustal deformation measurement combining th... more We have developed an observation system for seafloor crustal deformation measurement combining the two following techniques: the precise acoustic ranging and kinematic GPS (Global Positioning System) positioning. On July 14, 2003, we installed the units for this observation system at the seafloor of the Kumano Basin, Japan (33.58°N, 136.60°E). We performed repeated observation six times on 1
Earth and Planetary Science Letters, 1997
Attenuation structures were determined for the Philippine archipelago by inversion of earthquake ... more Attenuation structures were determined for the Philippine archipelago by inversion of earthquake intensity data set from 1957 to 1992. The intensity data based on the Adapted Rossi-Fore1 Intensity Scale were translated into acceleration values using a modified acceleration-intensity equation. A damped least-squares method was used in our inversion. We correlated the inversion results with other data, such as observed anomalous intensity distribution, present seismicity, and the location of trenches and volcanic centers. Our results strongly indicate the association of low attenuation values with subducted slabs along the known location of trenches in the Philippines. For example, the configuration of the Philippine Trench is suggested by the concentration of low attenuation values along the east side of central and southern Philippines while on the western side of Luzon Island a low attenuation structure is consistent with the location of the Manila Trench. The extent and depth of low attenuation values are also apparent along the eastern side of Luzon. In southern Luzon through Negros Island in the central Philippines, the site where anomalous intensity distribution was observed coincided with the location of a noticeable low-attenuation structure determined in this study. Moreover, possible locations of an upwelling magmatic body along the numerous areas in the Philippines are also indicated by the concentration of high attenuation values. Furthermore, a possible aseismic slab, which probably represents a structure that connects the Manila Trench with the Negros Trench, was also inferred in Eastern Mindoro. However, it is also possible that these low attenuating values are due to the presence of continental material in this area. On the basis of these initial results, we suggest some modifications of the configuration of tectonic structures in several portions of the archipelago.
Geophysical Research Letters, 1995
Depths of the partially melted zone and the Moho discontinuity are probably at 18 kilometers and ... more Depths of the partially melted zone and the Moho discontinuity are probably at 18 kilometers and 34 kilometers, respectively beneath Tagaytay seismic station, Luzon, Philippines. This conclusion is based on the shear-wave velocity structure determined in this study, which indicates the presence of a low-velocity zone and high-velocity zone at these depths. The shear wave velocity model was derived from the inversion of five receiver functions of teleseismic earthquakes recorded by the broadband seismometer at Tagaytay. However, due to the very limited information to constrain our initial model, other models with comparable waveform fit were also obtained but with deeper low velocity zone and shallower Moho. introduction in this paper, we use the data recorded by a broadband Streckheisen (STS-2) seismometer in Tagaytay seismic station (Besanaetal., 1993; Fukao, 1991). Tagaytay station (TGY)is located about 10 km north of the Taal Volcano island and sits along the outer ridge of Taal caldera, Batangas in southern Luzon (Figure 1). To the east of the study area is the westwardsubducting Philippine Sea Plate and the Philippine Fault Zone (PFZ), while to the west is the eastward-vergent Manila Trench subduction zone. Forster et al. (1990) suggested that the volcanoes in the area belong to the Macolod Corridor, a structure thought to be a rift zone between the Manila Trench and the PFZ (Defant et al., 1988) or probably formed from crustal thinning and/or complex partial melting beneath Batangas area (Besana, 1995). Major structures that traverse the area include the northern Sibuyan Sea branch of the PFZ (Bischke et al., 1990) and the southern extension of the West Marikina Valley Fault (Daligdig et al., 1993; Wolfe and Self, 1983). Listanco (1994) analyzed the petrochemical characteristics of basalts at Taal Volcano and distinguished two basalt groups with distinct mineral assemblages and corresponding depths of crystallization/generation. The more dominant basalt group has an olivine-clinopyroxeneplagioclase assemblage that suggests a depth of crystalization of not more than 5 kb which is roughly 15-20 km deep while the minor rock group shows near-primary magma characteristics (high MgO, Ni, and low FeO/MgO) possibly generated at about 10-11 kb. Based on the presence of later phases and attenuated spectral amplitude of signals passing beneath the northeastern portion of Taal Volcano, the existence of reflectors at depths of 1 and 8 km in Taal was determined by Nishigami et al. (1994) using the fan-shooting Copyright 1995 by the American Geophysical Union. Paper number 95GL03319 0094-8534/95/95GL-03319503.00 technique. Other studies conducted in the area largely dealt on the geology and activity of Taal Volcano (Alcaraz and Datuin, 1974; Geronimo, 1988; Knittel and Defant• 1988; Torres et al., 1990). Therefore, the structure of the crust and uppermost mantle beneath TGY is almost unknown.
Resource Geology, 2005
ABSTRACT High seismic activity in the Philippines originates from tectonic convergence related to... more ABSTRACT High seismic activity in the Philippines originates from tectonic convergence related to surface and subsurface seismotectonic features. Based on earthquake data, the archipelago can be divided into the seismically-active Philippine Mobile Belt and the aseismic North Palawan Block. The latter represents a rifted continental fragment of the Eurasian margin that juxtaposed with the rest of island arc units in central Philippines. Earthquake hypocenter plots on planar and in vertical profiles show that the seismic events are associated with known seismotectonic features. In addition, data suggest that the collision zone between the North Palawan Block and the Philippine Mobile Belt is characterized by a decreased amount of hypocenters at > 100 km depths. Although field evidence favors the presence of a subducted slab or slabs beneath western central Philippines, these are difficult to image using the present seismicity distribution dataset.
Geophysical Research Letters, 2006
We have developed an observation system for seafloor crustal deformation measurement combining th... more We have developed an observation system for seafloor crustal deformation measurement combining the two following techniques: the precise acoustic ranging and kinematic GPS (Global Positioning System) positioning. On July 14, 2003, we installed the units for this observation system at the seafloor of the Kumano Basin, Japan (33.58°N, 136.60°E). We performed repeated observation six times on 1) July 15–16 and
Journal of Geophysical Research, 2008
We developed a new geodetic method of monitoring crustal deformation on the ocean floor. The meas... more We developed a new geodetic method of monitoring crustal deformation on the ocean floor. The measurements were conducted at two sites beneath the Pacific Ocean, near the Nankai Trough, where the Philippine Sea plate subducts into the Pacific plate. The first site was at a depth of 700 m in Suruga Bay, and the second one was at a depth of 2000 m in the Kumano Basin. At each survey site, three seafloor transponders, whose positions were repetitively measured, were deployed to define a benchmark unit. An ultrasonic signal was generated from a surface vessel drifting over the benchmark unit that was transmitting and receiving the signal and the replies from the transponders. Both sound speed structure and the benchmark unit positions were determined simultaneously using a tomographic technique. We repeatedly carried out measurements over the two sites. For the Kumano Basin we made six measurements from July 2004 to August 2005. The benchmark unit location's horizontal precision was 5 cm, and its vertical precision was 10 cm. For Suruga Bay we made five measurements, and the positions were less accurate, with horizontal variation of 7 cm and vertical variation of 16 cm. We investigated the reason for the decreased precision in Suruga Bay with a numerical experiment, and the results revealed that the geometry of the measurement, that is, the vessel's path, is one of the most important variables in our method. At the Kumano Basin a 21.5-cm southward displacement of the benchmark unit was detected just below the site before and after a large earthquake (Mw 7.5). Our observation system therefore proved itself capable of detecting seafloor crustal deformation associated with crustal activities in offshore areas.