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Open Access latitude and ). Initial and ). The earth- ◦ 1 Discussions ) 7.2 earthquake 2013 Sciences w , M Natural Hazards Hazards Natural and Earth System System and Earth Phivolcs ) 7.1 with focal depth of 20 km. Based w M 2104 2103 ) 7.2 occurring at 8:12 a.m. (local time) with the epi- w ects registered intensity VI in Hinigaran, Negros Occi- 1,2 ff M and R. Eco 1,2 ). Later reports coming from near the epicenter of the quake show im- 2013 , longitude, 6 km southwest of , ( ◦ This discussion paper is/has beenSystem under Sciences review (NHESS). for Please the refer journal to Natural the Hazards corresponding and final Earth paper in NHESS if available. National Instiute of Geological Sciences, University of the , C.P. GarciaDepartment corner of Science and Technology (DOST) – Project NOAH, Metro , Philippines Phivolcs Early morning atstruck 8:12 a.m. Bohol of Island in 15quake’s the October focus Central 2013, was Philippines124.07 a at region Magnitude 12 of km ( depth (Fig. with its epicenter located at 9.86 US52.06 million. Widespreadlimestone landslides region and during sinkholes thenities formed earthquake. as These in destabilized remain the hillside aare predominantly slopes, significant still landslide-dammed threat vulnerable rivers to to collapse, and commu- upcoming triggered incipient months possibly sinkholes by of aftershocks November and and heavy December. rains in the 1 Introduction A devastating earthquake struckquake Bohol, originated Philippines at on 12on km 15 the depth October surface from 2013. for an severalThe The kilometers unmapped earthquake earth- and reverse resulted with , maximum in which vertical 222 manifested displacement fatalities of with 3 m. damage to infrastructure estimated at Abstract Nat. Hazards Earth Syst. Sci.www.nat-hazards-earth-syst-sci-discuss.net/2/2103/2014/ Discuss., 2, 2103–2115, 2014 doi:10.5194/nhessd-2-2103-2014 © Author(s) 2014. CC Attribution 3.0 License. San Jose, Culasi, , ,( and Intensity III in earthquake was later revised toon Magnitude preliminary ( reports ontensity the VII earthquake (Philippine intensity, Earthquake ground Intensityother shaking Scale places, was or ground highest PEIS), shaking felt at e dental, at In- Intensity , Bohol. V In in City and La Carlota, Intensity IV in City, Roxas City, ages of centuries-old churches flattened to the ground and collapsed buildings (Fig. preliminary reports bytemblor the pegged USGS at Magnitude sent ( center a 2 few km minutes South after of the Nueva earthquake, Vida Sur, had Bohol, the Philippines. The USGS record on the 1 Velasquez street, U.P. Diliman, Quezon2 City 1101, Philippines Received: 3 November 2013 – Accepted: 10Correspondence February to: 2014 A. – M. Published: F. 18 Lagmay ([email protected], March [email protected]) Published 2014 by Copernicus Publications on behalf of the European Geosciences Union. Brief communication “The magnitude 7.2 Bohol earthquake, Philippines” A. M. F. Lagmay 5 20 15 25 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | , ). ). 3 ) with 1994 , ected by ff 5.7) earth- NDRRMC 2013b ected by the w , ). Two signifi- ff M 3 5.9 ( 5.6) earthquake was s w M NDRRMC M ) which depict the type of 7.2 earthquake and most w 5.5 ( a). There are other lineament M s 2012 3 Wells and Coppersmith , M 7.2 earthquake in Bohol. This earth- w shore areas southwest of Bohol Island M ff ). The reverse fault in also does ected. Out of the 41 bridges a 1 ff 2106 2105 ). It was originally believed to be the source Ekstrom et al. ; 2000 1981 , , ). The total estimated cost of the damage to infrastructure Phivolcs a). Lineament analysis of digital topography show northeast- 7.2 earthquake of Bohol, we propose to name the fault, the 1 w 2013b , M ). The length measurement of the raised wall due to reverse faulting Dziewonski et al. 4 7.2 earthquake but it would appear based on the locus of earthquake NDRRMC w M a). Focal mechanism solutions generated by the Global Centroid Moment Tensor ). The earthquake epicenters plot in a northeast-southwest trend spanning ap- 1 The nomenclature of newly discovered faults or geological formations for that matter, In the worldwide database of earthquakes, a 3 m displacement of a fault approxi- As of 4:00 p.m., 3 November 2013, 2779 aftershocks have been recorded by the of the aftershocks (Fig. tional Disaster Coordinating Council (NDRRMC) hasand reported 222 8 fatalities, missing. 976 injured Adestroyed, total with of 58 490 73 002 housesearthquake, houses partially 3 were a are damaged, still 14passable 512 not ( of passable which while were 2 totally out of the 18 roads damaged are still im- giving rise to intensities measuring VIII or higher. To date (3 November 2013), the Na- Inabanga Fault. This alsoany would other active prevent faults complications thatthe will in be temblor, the north discovered and of future mapped Bohol. should in the there large be area a too must be mapped out in detail when possible. are normally based on where theymunicipality are is best exposed where and the described.generated Because reverse Inabanga the fault was fatal first seen and archetypal for the fault that structures found in the northerntem part defined of by Bohol and the they large could number correspond to of a earthquakes fault triggered sys- by the main shock. These most likely to havequake been triggered responsible for more the thanthe 3198 epicenters aftershocks, of 94 thesethe of earthquakes southern which which part span were of more felt. Cebufound island, than But in do 100 the Inabanga km not trend municipality follow andnot exactly (see of reach account the Fig. nearly orientation for of the thethe strike-slip fault afternoon focal trace of mechanism the solution devastating of Bohol an event earthquake (see recorded Fig. in is currently being determinedresolution in imagery. the field and through lineament mappingmately using high- corresponds to aBased magnitude on 7.2 this, earthquake the ( fault seen very well exposed in Anonang, Inabanga is southwest-trending structures cutting across the northerning portion through of Bohol several Island, municipalities pass- ofvillage Bohol of in Anonang, the northern municipalityrecorded, portion displacement of of of Inabanga, the originally where island.to gently In there southwest-trending sloping the wall were to as flat severalters much ground aftershocks long formed as (Fig. a 3 m northeast- high and extends more than five kilome- were reported in 25 villages in Bohol and 13 villages in ( is 2 257 337 182 Philippine Pesos (US$ 52.06 million dollars). Landslide occurrences of the epicenters and initialnorth field of reports the that East an Bohol unmapped Fault fault were or responsible faults for the about 20–25 km reports of landslides damming rivers raising fears of possible floods. Philippine Institute of Volcanology2013b and Seismology, 75 of which were felt ( proximately 100 km from(Fig. mainly inland to o is the East Bohol Fault ( 2 Earthquake source When the 2013 earthquake happened, the only mapped active fault in Bohol Island (CMT) project ( slip movement of the earthquakewith fault, a show slight a right reverse faultcantly lateral (dominant large strike-slip aftershocks vertical component recorded motion) for at the 4:36had p.m. reverse main (local and shock time) strike-slip (Fig. on focal the mechanisms,quake day was respectively. of The a the reverse main fault-related aftershock shock related while to the strike-slip fault movement based on their focal mechanism solutions (Fig. 5 5 25 20 15 10 10 25 15 20 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | , ). ). The Phivolcs 1982 ). Another 1990 , , 1996b , Holloway ), which straddles the Umbal et al. nity ( Phivolcs ffi 1962 ). , 5 Allen ; Gervasio, 1967), bound on both 5 2108 2107 ). Southwest of the PMB is the -Mindoro ). ). The most recent fatal temblor is the 2013 Bohol 1986 , 2009 6.9 earthquake generated by an unmapped thrust fault , ) formed through plate interaction of the Philippine Sea b M 2013a , 2004 Huchon , Lagmay et al. NDRRMC Encarnación ). The trenches in the east and west of the archipelago are major sites of seismicity and The entire archipelago is characterized by a system of subduction zones, collision subduction zones is the left-lateral Philippine Fault ( Trench, Trench, and Trench. In between these west- and east-dipping scale in the town of Jagna, Duero and Guindulman in Bohol ( The East Bohol Fault wasFebruary responsible 1990, for which generating generated the tsunamisthe M6.8 as southeastern Bohol high coast as earthquake of 2 on the mlocated 8 island. and 17 The significant km inundation epicenter east in of of the Tagbilaran City 1990 with Bohol earthquake intensities was reaching VIII on the Rossi-Forrel 3 Past earthquakes entire length of the PMB. Thereactive are faults many in active the faults in Bohol the region,Fault archipelago are and but the the the Cebu closest lineaments, West Centralmodate Negros the fault. Fault, stress The imparted tectonic byPlate structures the towards ongoing in Eurasia northwest ( the movement Philippines of accom- the Philippine Sea block, an aseismic region of the Philippines of continental a Sulu Sea is consumed whilePlate the subducts Philippine ( trench is the site where the Philippine Sea and referred to as aearthquake hidden fault, caused struck considerable Negros damage Islandsumed immediately killing west dead 51 of ( Cebu. people That earthquake, with which 62 released missing and underground, pre- tremendous amount of energy equivalent where marginal basins surroundingSea, the Sulu Philippines Sea are andNegros consumed. the and The Celebes Cotabato South trenches, Sea China respectively. Basins The subduct Sulu along Trench is the the east-dipping locus Manila, where the by Phivolcs are near urban centers,is populated by the millions second of people. most Metrocame populous Cebu, out which Metropolitan relatively area in unscathedBohol the with Island Philippines where only after the 12ary Metro earthquake deaths 2012, Manila, emanated. compared a A to shallow year focus the and 209 a fatalities half earlier, in on 6 Febru- 5 Conclusions The Bohol earthquakefaults is that a straddle the devastating Philippinemapped event islands. and that There are are emanates potential many from active sites faults for one that devastating of have earthquakes. been the Many active many faults listed to the eastern marginterranes of ( the EurasianPlate, Plate. Eurasian It Plate and is the composed Indo-Australian of Plate (Fig. a complex mixture of generally due to groundto shaking. other There earthquake were hazardsany no such other reports geologic as and ground liquefaction, observations1996b disturbances ground attributed during subsidence, the landslide 1996 and Bohol earthquake ( 4 Tectonic framework of the Philippines The Philippine archipelago is a mature island arc that is at present being accreted ple were displaced with at1990 least Bohol earthquake 7000 was rendered estimated homeless.Magnitude at Damage 5.6 154 to million earthquake property pesos struck ( for onity the 27 of May Clarin, 1996 Bohol. andbuilt Damage was structures centered brought and/or in by old the the wooden, municipal- 1996 masonry, limestone earthquake walls was of confined houses to and poorly buildings, temblor exacted six fatalities with more than 200 injured. Approximately 46 000 peo- known as the Philippinesides Mobile by Belt subduction zones. or West-dipping PMBand subduction (Fig. zones the are the Philippine East Trench. Generally Trough east-dipping subduction zones are the Negros zones, and wrench faults. The actively deforming region of the Philippines is a zone 5 5 10 25 15 20 20 15 10 25 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | , 2105 2106 2107 http://www.phivolcs.dost.gov.ph 2107 2105 2110 2109 2108 2108 2107 ects of Magnitude 7.2 Sagbayan, Bohol earthquake, National Dis- ects of the 6.9 earthquake in Negros Oriental. National Disaster Risk ff ff 2105 We wish to acknowledge the DOST-Project Nationwide Operational As- 2105 2108 2104 2108 earthquake in Bohol Province, Internal report, 1990. rupture area and rupture displacement, B. Seismol. Soc. Am., 84, 974–1002, 1994. 2013. magnitude, new empirical relationships among magnitude mw, rupture length, rupture width, May 1996, Online, 1996b. aster Risk Reduction and2013), Management 2013b. Council, available online (last access: 3 November Definition of Philippine PlateGeol. Soc. Boundaries Philippines, and 64, Implications 17–30, 2009. to the Philippine Mobile Belt, J. 1986. Reduction and Management Council, available online2108 (last access: 21 October 2013), 2013a. 1967. Mindoro to the AsianAAPG mainland Bull., and 66, its 1357–1383, significance 1982. in the evolution of the South China Sea, 4812, 1962. ters from waveform data for2825–2852, studies 1981. of global and regional seismicity, J. Geophys.moment Res., tensors 86, for 13,017 earthquakes, Phys. Earth Planet. In.,growth 200/201, of 1–9, an 2012. island complex, Tectonophysics, 392, 103–130, 2004. cent events are a wakeearthquakes up that call may for strike all the country residents elsewhere, of anytime. the Philippines to brace for possible an earthquake, can only beof built time, up again perhaps on aand the hundred same best fault years seen system or in overimminent a Inabanga, more. danger long Bohol, In period from in the most earthquakeand meantime, probability, further hazards the will destabilization sans reverse be of landslides fault quiet already found triggered and weakened will by ground not aftershocks and pose infrastructure. These re- to more than 30 Hiroshima atomic bombs. That amount of energy, which can trigger Umbal, J., Masigla, L., Medrano, R., and Diolata, G.: Report of Investigation on the Feb. 8, 1990 Wells, D. and Coppersmith, K.: Maximum surface fault displacement vs. earthquake moment Phivolcs: Compilation of damaging earthquake of the Philippines – Bohol Earthquake – 27 Phivolcs: Philippine Earthquake Intensity Scale (PEIS), Poster, 1996a. Phivolcs: Active Faults of thePhivolcs: Philippines, Primer Map, 2000. on the 2013 Bohol earthquake, available at: Lagmay, A., Tejada, L. G., Pena, R. E., Aurelio, M., Davy, B., David, S., and Billedo, E.: New NDRRMC: Sitrep 35 re E Huchon, P.: Comment on “The Kinematics of the Philippine Sea Plate”, Tectonics, 5, 165–168, NDRRMC: Sitrep 22 re E Holloway, N.: The stratigraphic and tectonic relationship of Reed Bank, north Palawan and Allen, C.: Circum-Pacific faulting in the Philippines- region, J. Geophys. Res., 67, 4795– Encarnación, J.: Multiple ophiolite generation preservedGervasio, in F.: the Age northern and Philippines nature and of the orogenesis in the Philippines, Tectonophysics, 4, 379–402, References Dziewonski, A., Chou, T., and Woodhouse, J. H.: Determination of earthquake source parame- Ekstrom, G., Nettles, M., and Dziewonski, A. M.: The global CMT project 2004–2010: centroid- Acknowledgements. sessment of HazardsBohol (NOAH) island DREAM and component for providing program fieldwork for funds. the 10 m resolution DEM of 5 5 20 15 10 25 15 20 10 3 7.2 w SE. ◦ J. Name 7.2 as measured w E dipping 82 ◦

Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Formerly gently sloping ground split through re- Focal mechanism solution of earthquakes recorded 7.2 Ina- w M nes (B) nes ile the Figure 3. on A) 15 October 2013 in Bohol and B) prior to the M Figure 4. verse faulting into aning upthrown block a and 3 lower meter blockPhoto: high form- AMF wall Lagmay. that extends for several kilometers. ing VIII on theDuero Rossi-Forrel and scale in Guindulman the inThe town temblor Bohol exacted of six (Umbal Jagna, fatalities et withjured. more al., Approximately than 46,000 1990). 200 people in- were displaced with in Bohol. The meanon principal 20 orientation measurements of of the its fault plane is based N39 Bohol earthquake (black beachballs). C)diagram Stereo plot of and the rose fault that generated the M www.jn.net 7.2 earthquake in Bohol. This w pth according to Phivolcs as of 20 October 2013 In the worldwide database of earthquakes, a 3 m 7.2 earthquake with a depth 12 km B) intensities in Bohol northern portion of the island. Inmunicipality of the Inabanga, village where of there Anonang, wereshocks several after- recorded, displacement ofing originally to gently slop- flattrending ground wall formed asmore a much than northeast- as five to 3measurement kilometers of southwest- long meters the (Figure high raisedis 4). and wall currently The due extends being length tolineament determined reverse mapping in faulting using the high-resolution field imagery. and through displacement of aa fault magnitude approximately 7.2 corresponds1994). earthquake Based to on (Wells this, and theBarangay Anonang, Coppersmith, fault Inabanga seen is very most well likelyresponsible to exposed have in been for the M earthquake triggered more thanwhich 3198 were aftershocks, felt. 94 But of theearthquakes trend which of span the morereach epicenters than of nearly these 100 the kilometersfollow southern and exactly part the of orientation ofInabanga Cebu the municipality island, fault (see trace do Figure foundin 1). not in Inabanga The also reverse does fault cal not account mechanism for solution thethe strike-slip of afternoon fo- of an the3A). earthquake devastating Bohol There recorded event are (see in othernorthern figure lineament part structures of found Boholfault in and system the defined they by could the correspond large number to of a earthquakes w M are lineaments in the shaded relief image of Bohol island, wh 2112 2111 5.7) w A.M.F. Lagmay: Magnitude 7.2 temblor rocks Bohol, Philippi 5.9 (M s intensities in Bohol and adjacent cities and municipalities. collapsed house in Sagbayan municipality, Bohol. (B) (A) Images of the disaster: A) collapsed house in Sag- 7.2 earthquake of Bohol, we propose to name the epicenters in Bohol and their corresponding depth according to Phivolcs 7.2 earthquake and most of the af- w w 7.2 earthquake but it would appear w (A) The nomenclature of newly discovered faults or geo- 5.6) earthquake was related to strike-slip w A.M.F. Lagmay: Magnitude 7.2 temblor rocks Bohol, Philippi Figure 2. bayan municipality, Bohol.Photos: B) AMF Inabanga Lagmay. church in Bohol. triggered by the main shock.out These in too must detail be when mapped possible. logical formations for that matter, arewhere normally they based are on bestabanga exposed municipality and is described. where Becauseseen In- the and reverse archetypal fault for wastal the first M fault that generated the fa- fault, the Inabanga Fault. Thisplications also in would the prevent future com- shouldfaults there that be will any be otherarea active affected discovered by and the mapped temblor, in north the of large Bohol. 3 Past earthquakes The East Bohol Fault wasM6.8 responsible Bohol for generating earthquake the onerated 8 February 1990, as which high gen- undation as in 2 the metersepicenter southeastern and of significant coast the in- of 1990kilometers east Bohol the of earthquake Tagbilaran island. City was with The intensities located reach- 17 www.jn.net Earthquake A) epicenters in Bohol and their corresponding de 5.5 (M s (Online list of recent earthquakes). The largest circle is the Figure 1. 2 earthquake was a reversethe fault-related M aftershock while fault movement basedtions on (Figure their 3). focal mechanism solu- 2 Earthquake Source When the 2013 earthquakeactive happened, the fault only mapped in(Phivolcs, Bohol 2000). Island Itsource is was of the originally the believed East M to Bohol be Fault the tershocks (Figure 1a). Lineamentpography analysis show of northeast-southwest-trending structures digitalcutting to- across thepassing through northern several portion municipalities of of Bohol Bohol in Island, the based on the locusfield of reports earthquake that epicenters20-25 and an kilometres initial north unmapped ofsponsible the fault for East or the Bohol M Fault faults were re- about J. Name and adjacent cities and municipalities. Dashed black lines solid black line in the south is the East Bohol Fault. sor (CMT) projectet (Dziewonski al., et 2012) which al.,the depict 1981; earthquake the Ekstrom type fault,vertical of show slip motion) a movement with of component reverse a for fault the slight (dominant maincantly right large shock aftershocks lateral recorded (Figure at 3). 4:36 strike-slip on PM Two (local the signifi- time) dayslip of focal the mechanisms, respectively. main The shock M had reverse and strike- Images of the disaster: Earthquake banga church in Bohol. Photos: AMF Lagmay. Fig. 2. Fig. 1. as of 20earthquake October with 2013 a (Online depthDashed list 12 km black of lines recent areblack earthquakes). lineaments line in in The the the largest south shaded is circle relief the is image East of Bohol the Fault. Bohol island, while the solid Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 3 7.2 3 w SE. 7.2 ◦ w SE. ◦ J. Name J. Name SE. ◦ 7.2 as measured Stereo plot and rose diagram 15 October 2013 in Bohol and 7.2 as measured w w (A) (C) E dipping 82 E dipping 82 ◦ ◦ E dipping 82 ◦ 2114 2113 7.2 as measured in Bohol. The mean principal orientation of w M Formerly gently sloping ground split through re- Focal mechanism solution of earthquakes recorded Formerly gently sloping ground split through re- Focal mechanism solution of earthquakes recorded 7.2 Bohol earthquake (black beachballs). nes w M Figure 3. on A) 15 October 2013 in Bohol and B) prior to the M Figure 4. verse faulting into aning upthrown block a and 3 lower meter blockPhoto: high form- AMF wall Lagmay. that extends for several kilometers. ing VIII on theDuero Rossi-Forrel and scale in Guindulman the inThe town temblor Bohol exacted of six (Umbal Jagna, fatalities et withjured. more al., Approximately than 46,000 1990). 200 people in- were displaced with in Bohol. The meanon principal 20 orientation measurements of of the its fault plane is based N39 Bohol earthquake (black beachballs). C)diagram Stereo plot of and the rose fault that generated the M nes Figure 4. verse faulting into aning upthrown block a and 3 lower meter blockPhoto: high form- AMF wall Lagmay. that extends for several kilometers. ing VIII on theDuero Rossi-Forrel and scale in Guindulman the inThe town temblor Bohol exacted of six (Umbal Jagna, fatalities et withjured. more al., Approximately than 46,000 1990). 200 people in- were displaced with Figure 3. on A) 15 October 2013 in Bohol and B) prior to the M in Bohol. The meanon principal 20 orientation measurements of of the its fault plane is based N39 Bohol earthquake (black beachballs). C)diagram Stereo plot of and the rose fault that generated the M Formerly gently sloping ground split through reverse faulting into an upthrown block and Focal mechanism solution of earthquakes recorded on prior to the Fig. 4. lower block forming a 3 m high wall that extends for several kilometers. Photo: AMF Lagmay. of the fault that generatedthe the fault based on 20 measurements of its plane is N39 Fig. 3. (B) Images of the disaster: A) collapsed house in Sag- 7.2 earthquake of Bohol, we propose to name the w The nomenclature of newly discovered faults or geo- A.M.F. Lagmay: Magnitude 7.2 temblor rocks Bohol, Philippi Figure 2. bayan municipality, Bohol.Photos: B) AMF Inabanga Lagmay. church in Bohol. triggered by the main shock.out These in too must detail be when mapped possible. logical formations for that matter, arewhere normally they based are on bestabanga exposed municipality and is described. where Becauseseen In- the and reverse archetypal fault for wastal the first M fault that generated the fa- fault, the Inabanga Fault. Thisplications also in would the prevent future com- shouldfaults there that be will any be otherarea active affected discovered by and the mapped temblor, in north the of large Bohol. 3 Past earthquakes The East Bohol Fault wasM6.8 responsible Bohol for generating earthquake the onerated 8 February tsunamis 1990, as which high gen- undation as in 2 the metersepicenter southeastern and of significant coast the in- of 1990kilometers east Bohol the of earthquake Tagbilaran island. City was with The intensities located reach- 17 www.jn.net Images of the disaster: A) collapsed house in Sag- 7.2 earthquake of Bohol, we propose to name the w The nomenclature of newly discovered faults or geo- A.M.F. Lagmay: Magnitude 7.2 temblor rocks Bohol, Philippi Figure 2. bayan municipality, Bohol.Photos: B) AMF Inabanga Lagmay. church in Bohol. triggered by the main shock.out These in too must detail be when mapped possible. logical formations for that matter, arewhere normally they based are on bestabanga exposed municipality and is described. where Becauseseen In- the and reverse archetypal fault for wastal the first M fault that generated the fa- fault, the Inabanga Fault. Thisplications also in would the prevent future com- shouldfaults there that be will any be otherarea active affected discovered by and the mapped temblor, in north the of large Bohol. 3 Past earthquakes The East Bohol Fault wasM6.8 responsible Bohol for generating earthquake the onerated 8 February tsunamis 1990, as which high gen- undation as in 2 the metersepicenter southeastern and of significant coast the in- of 1990kilometers east Bohol the of earthquake Tagbilaran island. City was with The intensities located reach- 17 www.jn.net Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | nes www.jn.net Argao Fault; = Laur Dingalan Fault (Lagmay et = chipelago. B) Major tectonic features of the Philip- River Fault; VA = The entire archipelago is characterized by a system =Vigan Agao Fault; C=Cordilleran Fault; P=Pugo Fault; Eurasian Plate. Itof is terranes composed 2004) (Encarnaci´on, ofinteraction formed of a through the complex plate Philippineand mixture Sea the Plate, Indo-Australian Plate Eurasian (Figure Plate 5). of subduction zones, collisionThe zones, actively and wrench deformingzone faults. region known as of the Philippine theure Mobile 5); Belt Philippines Gervasio, or 1967), is PMB boundtion (Fig- on a zones. both West-dipping sides subduction byLuzon zones subduc- are Trough the East andeast-dipping the subduction zones PhilippineSulu are Trench. Trench, the Generally and Negroswest- Cotabato Trench, and Trench. In east-dippinglateral between Philippine subduction these Fault zonesthe (Allen, entire 1962), is length which thefaults straddles of in left- the the PMB. archipelagothe but There Bohol the region, are closest are many active the faults active Cebu in lineaments, Central Ne- B) of Gervasio (1967). The stippled gray shaded area is the 2115 Digdig Fault; LD A.M.F. Lagmay: Magnitude 7.2 temblor rocks Bohol, Philippi = Pugo Fault; D = A) Map showing the main plates surrounding the Philippine Ar Figure 5. 4 pines. The gray shadedPalawan-Mindoro area continental is block. the AR=D=Digdig Philippine Abra Fault; LD=Laur Mobile River Dingalan Belt Fault; Fault. (PM VA Lagmay et al., 2009 at least 7,000for rendered homeless. the Damage 1990million to pesos Bohol property (Phivolcs, earthquake 1996b).earthquake Another was Magnitude struck estimated 5.6 on 27 atthe May municipality 154 1996 of and was Clarin,the centered 1996 Bohol. in earthquake Damage was broughttures confined by to and/or poorly old builthouses struc- wooden, and masonry, buildings, limestone generallyThere due walls were to of no groundother shaking. reports earthquake and hazards observationssubsidence, such landslide attributed as and to any liquefaction, otherturbances ground geologic during ground the dis- 19961996b). Bohol earthquake (Phivolcs, 4 Tectonic Framework of theThe Philippines Philippine archipelago isis at a present mature being island accreted to arc the that eastern margin of the J. Name Map showing the main plates surrounding and major tectonic features of the Philippines. Cordilleran Fault; P = The gray shaded area is thearea Philippine is Mobile the Belt Palawan-Mindoro continental (PMB) of block. AR Gervasio (1967). The stippled gray Fig. 5. al., 2009). C