Rupture Process of the M7.2 October 2013 , Earthquake

Acknowledgement: Tomokazu Kobayashi Muriel Naguit1, Phil R. Cummins1,2 and Bart Bautista3 1Research School of Earth Sciences, Australian National University 2Geoscience , Canberra, Australia 3Philippines Institute of Vulcanology and Seismology Outline

• Development of a rupture model – M7.2 October 2013 Bohol earthquake – Joint inversion of multiple datasets (seismic waveforms & SAR radar image) • Post-damage assessment – Correlate observed ground motions with damage observations – Constrain & validate building fragility curves & vulnerability models

2 The 2013 M7.2 Bohol Earthquake • Event: October 15, 2013 at 8:12:31 AM local time • Casualties: 210 fatalities & 877 injuries • Structural damage: 71,885 totally & 57,405 partially damaged • Cost: up to US$53M, US$34M of which was infrastructure damage

3 NEIC Finite Model SE dipping rupture plane consistent with geologic & SAR data. Most slip concentrated at asperity SW of hypocentre, and offshore Bohol.

4 Kobayashi et al. SAR Fault Model

• Kobaysashi et al. (2014) used RADARSAT data to resolve coseismic displacement • Heavy vegetation precluded the use of conventional InSAR, so pixel tracking was used. • Inferred strike and dip are differ considerable w.r.t seismic estimates • Coseismic uplift appears distributed almost evenly along strike

5 Joint Seismic/SAR Fault Model

6 Use of Exsim to Model Ground Motions From USGS From EXSIM

7 Local Geology

Metavolcanics or metamorphosed submarine flows

Marine pyroclastics

Marine & terrestrial sediments

Source: Mines & Geosciences Bureau, Philippines 8 Earthquake damage, etc.

Source: Bacolcol,T., et al. (2014) 9 Strong Motion Recorded at

• 1g peak-to-peak • Limestone platform • No obvious topographic influence • Shakemap intensity about IX

10 Damage to buildings was extensive

Source: GFZ and KIT (2013)

11 Accessibility and Previous Damage Surveys

A few damage surveys were done in the months following the event, but none produced a statistical survey of damage – i.e., no exposure, so can’t be used to constrain fragility curves.

The area is in general highly vegetated, and many communities are difficult to access by road.

12 Development of Exposure Database Field Reconnaissance Visit the hardest hit municipalities located in the western part of Bohol. Introduce the research to local agencies .

Site Selection & Collection of Spot Maps Factors in site collection include (1)intensity levels; (2) urban & rural areas; (3)population; and (4) reports on damaged & destroyed structures

Conduct of Interview in Pilot Sites & Short‐term Agreement w/Universities A test run was conducted to check the adequacy of the survey process and completeness of survey form. Two universities have agreed to assist in data collection ‐the and the .

Actual Survey/Interview The interview involves the barangay officials and health workers. Using the spot map as guide, each structure in a chosen barangay is characterized .

Completion of Exposure Database The final exposure database consisted of 18,028 structures coming from 61 barangays (18 urban & 43 rural) in 20 municipalities of Bohol, Philippines.

13 Site Selection

• Employed local university students • Sampled Intensities from VI to IX • Sampled mix of urban and rural

14 Interviews with local officials & health workers

15 Survey Form Structural attributes incorporated in the survey form rop‐down menu

Sample exposure database

16 Mix of construction types

tholic Church in Two‐storey commercial building School compound in Municipal Hall in Guindulma n In Ubay

Small chapel in Carmen A house using steel frame with Two‐storey house that sustained Confined masonry house wooden sheets in damage in in Tagbilaran

xed wooden‐hollow block type Concrete hollow block house Typical nipa hut in Villalimpia A three‐storey wooden hous In Toril, Maribojoc with nipa roofing in Poblacion, Maribojoc

17 Objective: Constrain Fragility Curves

C1‐LC1‐M

S1‐LS1‐M

Reference: Universit y of the Phili pp ines Diliman‐Institute of Civil En gineerin g, GMMA‐RAP Pro ject , Develo pment o f 18 Summary of Exposure Database

19 Preliminary Analysis: Damage vs. Construction Era

20 Preliminary Analysis: Damage vs. Wall Type

21 Future Work

• We hope to extend the dataset used for source model construction to include GPS data as well as empirical Green’s functions. • The remaining Barangays in Bohol will be “paintbrushed” with the distributions of building types, etc. that were found in this survey. • Damage data will be analysed to separate out fragility curves for different building types and eras.

22 Conclusions • Joint inversion of multiple datasets, including seismic waveforms, satellite radar images & GPS observations should result in a robust source model of the 2013 Bohol Philippines earthquake. • The post-event damage assessment would hopefully complement the source model in explaining the damage pattern. Consequently, the rupture model may also aid in validating the building fragility curves. • Through the validation of building fragility curves, we expect hat more robust impact forecasts can be made for earthquakes in the Philippines and elsewhere, and that this may led to greater investment in seismically resilient building construction practices.

23 Questions?

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