MINES AND GEOSCIENCES BUREAU Regional Office No - MGB-XI

Republic of the Philippines
Department of Environment and Natural Resources
MINES AND GEOSCIENCES BUREAU
Regional Office No. XI
669 Konsuela Bldg., Aurora Quezon Street, Davao City
Tel. No. (082) 222-5601 Telefax No. (082) 221-6535 Email: [email protected]
GEOHAZARD IDENTIFICATION REPORT ON THE PROPOSED SHRINE OF THE
BLESSED VIRGIN MARY AT BARANGAY BADAS, CITY OF MATI ,
DAVAO ORIENTAL
1.0 INTRODUCTION
By nature of its geological and climatological setting, natural hazards such as landslides,
flooding, earthquakes, typhoons and volcanic activities are far more common in our country.
Having realized the impact of these hazards in socio, environmental, and economical
perspective, the Government, constant of its aims of protecting its people, mandated that all
subdivisions, housings, land developments and infrastructure projects must undergo
geohazard site assessment1. The assessment includes the identification of possible
geologic hazards within and adjacent areas of the project to be developed and suggest
measures that may be considered to reduce, if not, mitigate its effects and impacts.
In response to the letter request of Hon. Governor Corazon N. Malanyaon of Davao
Oriental, a geohazard identification survey was conducted in the proposed Shrine of
Blessed Virgin Mary at Brgy. Badas, Mati City. The site is more or less 1,000 square meters
and is a portion of Lot No. 4091, Psd-11-025713 (AR) that is covered by Transfer Certificate
of Title No. CLOA No. 219. The said property was donated to the Daughters of the Mary
Immaculate, International.
Prior to the conduct of the site inspection, review of related studies such as geologic reports
and geologic and geohazard maps were done to provide background information of the
project area. During the field survey, actual identification and delineation of the geologic
hazard were done. Accurate location of the data points were gathered using Garmin
GPSmap 76CSx and were plotted to a blown up 1:7,000 from 1:50,000 scale topographic
map of NAMRIA Mati Quadrangle Sheet 4240-IV.
The report presents the results of the conducted assessment and some technical
recommendations for the proponent to consider upon development.
2.0 LOCATION AND ACCESSIBILITY
The proposed shrine is located in Purok 1, Brgy. Badas, City of Mati, Davao Oriental
Province. The site is proximal to the national highway and is approximately centered in
geographic coordinates 125°54'21.7" east longitude and 7°54'23.2" north latitude. It is more
or less 7.1 kilometers (linear distance) southwest from the City Hall of Mati and can be
1
DENR Administrative Order No. 2000-28 " Implementing Guidelines on Engineering Geological and Geohazard Assessment as Additional
Requirement for ECC Applications covering Subdivision, Housing and other Land Development and Infrastructure Projects”, DENR, March 14, 2000
access by any type of private or public vehicles through the Diosdado Macapagal National
Highway.
Point Boundary
1
2
3
4
Geographic Coordinates
Datum (Luzon 1911)
126°10'18.322"E 6°54'15.999"N
126°10'18.02"E 6°54'14.786"N
126°10'17.321"E 6°54'15.136"N
126°10'17.609"E 6°54'16.212"N
Table 1: Geographic coordinates of the proposed site
Fig 1: Satellite image of the proposed Shrine of the Blessed Virgin Mary (see red polygon) in Po. 1, Brgy. Badas, Mati City, Davao
Oriental. (Google Image 2013, Image looking southwest direction)
3.0 CLIMATE AND VEGETATION
City of Mati falls within the Type IV
climate based on Modified Corona’s
Climate
Classification
of
the
Philippines characterized by more or
less evenly distributed rainfall and
having no dry or wet season (Fig 2).
Within the vicinity of the project site,
tropical trees and plants such as
Coconut, Ipil-ipil, corn, grasses and
shrubs are observed.
Fig 2: Climate Map of the Philippines based on the Modified
Coronas Classification
4.0 TOPOGRAPHY AND DRAINAGE
The proposed Shrine of the Virgin Mary is situated on a rugged terrain and bounded by very
steep slopes at the western and eastern portion with narrow north-south trending ridge. The
main drainage networks of the area are gullies that incised the very steep mountain slopes
and drains towards Pujada Bay (Fig 3).
Fig 3: Topographic Map of the Proposed Shrine of the Blessed Virgin Mary
5.0 GEOLOGY
5.1 REGIONAL GEOLOGIC SETTING
The proposed site is within the southern Pacific
Cordillera. The region consisting of several
massifs in tectonic (?) contact with one another
is affiliated either with the Philippine Arc or
Pujada Ophiolite. The Pujada Peninsula Block
is composed of six (6) formations (Fig.4)
namely Pujada Ophiolite, Iba Formation,
Basiaw Limestone, Sanghay Formation,
Sigaboy Formation and Maco Limestone. The
oldest formation in the area is the Low
Cretaceous to Upper Cretaceous Pujada
Ophiolite and the youngest is the Middle to Late
Pleistocene Maco Limestone (MGB, 2010).
According to Arcilla et al.2, the central Pujada
Peninsula is composed of series of imbricated
segments of ophiolitic rocks. The Upper
Cretaceous Iba Formation and Lower Miocene
Sanghay Formation were folded into series of
synclines and anticlines. A broad anticline is
formed east of the central Pujada Peninsula.
Further, the east-west compressive forces in
the northeast of the Pujada Peninsula could
have persisted even after the Miocene
(?) time as the warped Upper Cretaceous
volcanic sedimentary rocks and the Lower
Miocence greywacke sediments have still
experienced folding.
The region is traversed by the Philippine Faulta left lateral strike slip fault. One of its major
splays exits at the southwestern coastline of
Pujada Bay. Mati Fault on the other hand,
trends northwest along the rugged terrain of
Kalampuyagan to southwest of Taguibo at the
headwaters of Bitanagan River (Fig. 5).
Fig 4: Stratigraphic Column of Pujada Peninsula (MGB)
This Site
Fig 5: Neotectonic of Mindano (Publier, et al.) showing the
proposed Shrine of Blessed Virgin Mary
2
Arcilla D.M. and Narcos, D.M., Geology of Bato-Bato, Mati, Taganilao and Portion of Bitanagan Quadrangles, Davao Oriental, Bureau of Mines and
Geosciences, Regional Office No. X, Surigao City, April 1985
5.2 LOCAL GEOLOGY
Based on the Published Geology and Mineral Resource Map of this Office, the area is within
the thick sequence of slightly metamorphosed greywacke and siltstone with lenses of chert,
intercalated occasionally with basalts flows and intruded by diorite and ultramafic rocks with
Cretaceous in age (Fig 6). Field investigation indicates that the site is underlain by fine to
medium grained greywacke (sandstone) and dark brown mudstone. The lithologies are
observed to be fractured. The greywacke and mudstone probably represents the Sanghay
Formation that unconformably overlies the Iba Formation which is composed of basalts,
argillite, limestone, chert and clastic rocks on this portion of the Pujada Peninsula (MGB,
2010).
This
Site
Fig 6: Geologic Map of Davao Oriental
6.0 SITE DEVELOPMENT PLAN
Based on the submitted developmental plan, the proposed site will cover the following
development: altar, vestry and sacristy, an open atrium, statues of the Crucifix, Blessed
Virgin Mary and Sacred Heart of Jesus and comfort rooms. The site will cover more or less
1000 square meters of land area (Fig 7).
Fig 7: Site development plan of proposed Shrine of the Blessed Virgin Mary
7.0 ASSESSED GEOHAZARD
7.1 MASS MOVEMENT
The proposed site is situated on a ridge that is bounded by very steep slopes on the eastern
and western portion of the area. The area is subjected to creep, slope erosion, rill and gully
development. Based on the 1:10,000 Scale Geohazard Mapping and Assessment of Mati
City, the area is delineated to have moderate susceptibility to landslide (Fig. 8) Although the
area has moderate landslide susceptibility, alteration of the topography to accommodate the
desired development may affect the stability of the ground and may potentially lead to mass
movement. These maybe trigger by seismic activity or hydraulic action. Furthermore,
fracture lithology of the area may also contribute to ground instability.
Fig 8: Landslide Susceptibility of the proposed Shrine of the Blessed Virgin Mary
7.2 SEISMIC HAZARD AND GROUND SHAKING
The Philippines is situated in a tectonically active
region. Accounting some of the major fault zone
on Mindanao Island are the Philippine Fault and
its splay faults, Philippine Trench, Cotabato
Trench, Mindanao Fault, and other inferred
faults. The site is bounded by the splays of the
Philippine Fault, an active fault, on the western
and eastern portion from the property. The
western splay is approximately 3 kilometers from
the site while the eastern slay is approximately
7.3 kilometers from the site.
According to the Global Seismic Hazard Map of
the UN/International Decade of Natural Disaster
Reduction Study
(1998), the City of Mati has
4.8 values of Peak Ground Acceleration (m/sec2)
with 10% Probability of Exceeding in 50 years,
corresponding to return period of 475 years (Fig. 9)
Fig 9: Global Seismic Hazard Map of the Philippines
With the presence of the above mentioned earthquake generators, ground shaking as a
result of seismic activity may affect the area.
8.0 CONCLUSION AND RECOMMENDATION
Based on the results of the geohazard identification survey, certain geologic hazards were
identified in the area particularly mass movement and seismic-related hazard that may
potentially affect the area. These are influenced by the steepness of slope and fractured
lithology of the underlying material as well as the active splays of Philippine Fault that
traverses Mati City. The proposed development of Shrine of the Blessed Virgin Mary
may be undertaken provided that the following recommendation should be strictly followed
by the proponent, to wit:

A detailed geotechnical study (foundational analysis) should be undertaken to fully
evaluate the structural load and the condition of the underlying materials of the area.
This will also serve as guide for the appropriate design of the proposed development.

Appropriate engineering bioengineering and or bioengineering measure should be
undertaken on the slopes of the area for stability and minimized slope erosion.

Proper drainage system should be installed to efficiently channel and dispose run-off
water and minimized slope wash and erosion.

Proper grading procedures should be considered to maximize utilization of the land
area. Strict standards eg. (ASSTHO, NSCP) of grading procedures should be
followed to attain optimal stability and materials to be used as backfill should fit the
projects dominant layer.

Building or structural designs should be conform to the National Structural Code of
the Philippines (NSCP).
Prepared by:
ALLEN JUNE B. BUENAVISTA
Geologist
DOCUMENTATION
Photo 1: Ridge where the proposed Shrine of the Blessed
Virgin Mary is to be constructed.
Photo 2: Very steep slopes at the western portion of the
property.
Photo 3: Steep slopes characterized the surrounding area of the
proposed site
Photo 4: Fractured Greywacke (sandstone) observed in the
area.
Photo 5: Fractured mudstone underlying the area.
Photo 6: Panoramic view of the proposed site (encircle, looking
SW)