Subsurface Configuration of Western Masbate Island, Philippines 
from Integrated Gravity and Magnetics Data Inversion

Pearlyn C. Manalo1*, Carla B. Dimalanta1, Noelynna T. Ramos1,
Decibel V. Faustino-Eslava1,2, Karlo L. Queaño1,3, Betchaida D. Payot1 
and Graciano P. Yumul, Jr.1,3

1 Rushurgent Working Group, National Institute of Geological Sciences,
University of the Philippines, Diliman, Quezon City, Philippines
2School of Environmental Science and Management,
University of the Philippines – Los Baños, Philippines
3Monte Oro Resources and Energy Inc., Philippines


Acquired potential field data in western Masbate Island was investigated to characterize subsurface structures in the region. Gravity anomalies over areas with mapped intrusives are characteristically high, which could be attributed to huge density contrasts between the intrusives and the surrounding sedimentary formations. On the contrary, low to intermediate anomalies are observed overthe differentigneous rocks of the Balud Ophiolitic Complexin the southwestern section of the island. These nearly homogenous signatureis taken reflect the low density contrasts of the underlying mafic units.Asis usually expected, magnetic anomalies are higher over ophiolitic and instrusive rocks and lower over sedimentary formations. Further processing of potential-field geophysical data were carried out using various mathematical filtering techniques to delineate subsurface structures. Gravity and magnetic data were low-pass filtered to eliminate the effects of local shallow anomaly sources. The gravity anomalies were then deconvoluted using a 3D Deconvolution technique and subsurface contacts between different formations were delineated. Magnetic data were likewise processed for low-pass filtering and were subsequently processed for spectral analysis. The radially averaged power spectrum of the magnetic data allowed the calculation of the depth of the deepest magnetic sources, and eventually the delineation of the Curie point depth (CPD).The proposed subsurface model for western Masbate, using the combined magnetic and gravity information, is that of a crust that thickens to the northeastwith underlying rocks that lose their magnetic properties below a depth of 8km. The delineated crustal structure beneath Masbate island provides additional information for the regional characterization of the Central Philippines subsurface. Geophysical techniques used for subsurface imaging also exhibits potential application for resource exploration and geohazards assessment.

To get the whole report , please call (633-9025) or email us: 

Geological Society of the Philippines

Unit 250, 2nd Floor, Cityland Pioneer,

128 Pioneer Street, Mandaluyong City, Philippines

Tel: +(63-2) 633-9025