Risk-targeted seismic hazard model for the Philippines

Abstract

The Philippines' current seismic design framework, grounded in outdated uniform hazard approaches, fails to ensure consistent structural safety due to regional variations in seismic risk and structural fragility. This study aims to develop the first risk-targeted seismic hazard maps for the Philippines, adopting the ASCE 7-16 framework and integrating updated probabilistic seismic hazard data from the SHADE Project. Through the application of risk-integral formulations, the annual probability of structural collapse was computed by convolving seismic hazard curves and lognormal fragility functions. A parametric analysis was conducted using varying fragility dispersions (β = 0.6, 0.7, 0.8) and target collapse probabilities (P_fail) to evaluate their effects on risk coefficients (C_R), conditional collapse probabilities, and hazard curve slopes (η) for spectral accelerations at 0.2 s and 1.0 s. Results reveal that higher fragility dispersions and lower collapse targets significantly increase required design motions, particularly in short-period structures. The selected baseline parameters, β = 0.6 and P_fail = 2 × 10⁻⁴ (1 % collapse risk in 50 years), yielded consistent collapse probabilities and aligned with international standards. Spatial analyses showed elevated C_R in high-hazard zones such as Western Luzon, Eastern Visayas and Mindanao, while a strong correlation between C_R and η underscores the importance of hazard curve shape in seismic design. All computations assumed rock site conditions, with future work recommended to address site-specific effects.

Keywords

Risk-targeted ground motion / Sensitivity analysis / Seismic hazard mapping / Fragility curves / PSHA

CRediT authorship contribution statement

Rhommel Grutas: Writing - review & editing, Supervision, Project administration, Methodology, Funding acquisition, Conceptualization. Jhon Philip Camayang: Writing - review & editing, Writing - original draft, Visualization, Validation, Resources, Project administration, Methodology, Investigation, Formal analysis, Data curation, Conceptualization. Justine Anne Duka: Writing - review & editing, Validation, Investigation. Miguel Antonio Magandi: Writing - review & editing, Validation, Resources, Project administration, Methodology, Investigation. John Edward Nachor: Writing - review & editing, Validation, Resources, Methodology, Investigation. Jedrek Angelo G. Tupas: Visualization, Validation, Resources, Methodology, Investigation, Formal analysis. Guia Angela C. Agoncillo: Writing - review & editing, Resources, Investigation.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Author agreement and acknowledgments

The authors express their gratitude to the Department of Science and Technology - Philippine Institute of Volcanology and Seismology (DOST-PHIVOLCS), under the leadership of Dr. Teresito C. Bacolcol, Dr. Ma. Mylene M. Villegas, Sir Ishmael C. Narag and Dr. Winchelle Ian G. Sevilla, for serving as the implementing agency for this research. Acknowledgment is also extended to the Department of Science and Technology (DOST) as a funding agency for the SHADE Project and Department of Science and Technology - Philippine Council for Industry, Energy, and Emerging Technology Research and Development (DOST-PCIEERD) for their support as the monitoring agency. The contributions of Project SHADE staff, including Nicole Ann Bersabe, Montgomery van Brussel Toft, Rizza Micaela Padre, Koreen Dorado, and Louise Anthony Alparaque are sincerely appreciated-their commitment and teamwork were instrumental in addressing the complex challenges of seismic hazard assessment and ensuring the timely completion of this study.

References

[1] Applied Technology Council, 1978. Tentative Provisions for the Development of Seismic Regulations for Buildings:a Cooperative Effort with the Design Professions, Building Code Interests and the Research Community (No. NBS SP 510; 0 Ed., P. NBS SP 510). National Bureau of Standards. https://doi.org/10.6028/NBS.SP.510.

[2] Arada A.H., Majid T.A., Choong K.K., 2024. A step toward developing risk-targeted seismic design maps for Malaysia. Part 1: a representative exposure model. Arabian J. Sci. Eng. https://doi.org/10.1007/s13369-024-09822-9.

[3] Baker J.W., 2015. Efficient analytical fragility function fitting using dynamic structural analysis. Earthq. Spectra 31 (1), 579-599. https://doi.org/10.1193/021113EQS025M.

[4] Baker J.W., Bradley B., Stafford P., 2021. Seismic Hazard and Risk Analysis, first ed. Cambridge University Press. https://doi.org/10.1017/9781108425056.

[5] Bradley B.A., 2010. Epistemic uncertainties in component fragility functions. Earthq. Spectra 26 (1), 41-62. https://doi.org/10.1193/1.3281681.

[6] Butuan City Earthquake Model:Event-Based Probabilistic Seismic Risk Assessment, 2025. (with Philippine Institute of Volcanology and Seismology) 1. ISBN. https://www.phivolcs.dost.gov.ph/index.php/publications/books/seismic-hazard-and-ground-motion-atlases.

[7] Chen J., Wang W., Fang C., 2022. Seismic collapse capacity and dispersion spectra for self-centering braced frames considering uncertainty propagation. Earthq. Eng. Struct. Dynam. 51 (14), 3367-3392. https://doi.org/10.1002/eqe.3727.

[8] Cito P., Iervolino I., 2024. Drivers to seismic hazard curve slope. Earthq. Eng. Struct. Dynam. 53 (15), 4497-4510. https://doi.org/10.1002/eqe.4226.

[9] Cornell C.A., 1968. Engineering seismic risk analysis. Bull. Seismol. Soc. Am. 58 (5), 1583-1606. https://doi.org/10.1785/BSSA0580051583.

[10] Crowley H., Colombi M., Borzi B., Faravelli M., Onida M., Lopez M., Polli D., Meroni F., Pinho R., 2009. A comparison of seismic risk maps for Italy. Bull. Earthq. Eng. 7 (1), 149-180. https://doi.org/10.1007/s10518-008-9100-7.

[11] Douglas J., Ulrich T., Negulescu C., 2013. Risk-targeted seismic design maps for mainland France. Nat. Hazards 65 (3), 1999-2013. https://doi.org/10.1007/s11069-012-0460-6.

[12] El-Bahey S., Alzeni Y., 2016. Effect of soil structure interaction on the seismic fragility of a nuclear reactor building. Volume 1: Operations and Maintenance, Aging Management and Plant Upgrades; Nuclear Fuel, Fuel Cycle, Reactor Physics and Transport Theory; Plant Systems, Structures, Components and Materials; I&C, Digital Controls, and Influence of Human Factors. https://doi.org/10.1115/ICONE2460714.V001T03A021.

[13] Horspool N., Hulsey A., Elwood K., Gerstenberger M., 2021. Risk Targeted Hazard Spectra for Seismic Design in New Zealand.

[14] Iloilo city earthquake model: event-based probabilistic seismic risk assessment (vol.1) (with Philippine institute of volcanology and seismology), Department of Science and Technology - Philippine Institute of Volcanology and Seismology (DOST PHIVOLCS), 2023. https://www.phivolcs.dost.gov.ph/index.php/publications/books/seismic-hazard-and-ground-motion-atlases.

[15] Kennedy R.P., 1999a. Overview of methods for seismic PRA and margins analysis. Reliab. Eng. Syst. Saf. 65 (2), 171-179.

[16] Kennedy R.P., 1999b. Risk based seismic design criteria. Nucl. Eng. Des. 192 (2-3), 117-135. https://doi.org/10.1016/S0029-5493(99)00102-8.

[17] Kim T., Han S.W., 2021. Seismic collapse performance of steel special moment frames designed using different analysis methods. Earthq. Spectra 37 (2), 988-1012. https://doi.org/10.1177/8755293020970969.

[18] Luco N., Ellingwood B.R., Hamburger R.O., Hooper J.D., Kimball J.K., Kircher C.A., 2007. Risk-targeted versus current seismic design maps for the conterminous United States. SEAOC 2007 Convention Proceedings 13.

[19] McGuire R.K., 2004. Seismic Hazard and Risk Analysis. Earthquake Engineering Research Institute. https://books.google.com.ph/books?id=ZUVCAQAAIAAJ.

[20] Monti G., Demartino C., Gardoni P., 2023. Towards risk-targeted seismic hazard models for Europe. Sci. Rep. 13 (1), 10717. https://doi.org/10.1038/s41598-023-36947-y.

[21] National Structural Code of the Philippines 2015, 2016. Association of Structural Engineers of the Philippines, Inc (Seventh edition, Vol. 1) (with Association of Structural Engineers of the Philippines (ASEP)).

[22] Peñarubia H.C., Johnson K.L., Styron R.H., Bacolcol T.C., Sevilla W.I.G., Perez J.S., Bonita J.D., Narag I.C., Solidum R.U., Pagani M.M., Allen T.I., 2020. Probabilistic seismic hazard analysis model for the Philippines. Earthq. Spectra 36 (1_Suppl. 1), 44-68. https://doi.org/10.1177/8755293019900521.

[23] Philippine Earthquake Model (PEM): a Probabilistic Seismic Hazard Assessment of the Philippines and of Metro Manila (With Philippine Institute of Volcanology and Seismology (DOST-PHIVOLCS)), 2017. Department of Science and Technology Philippine Institute of Volcanology and Seismology.

[24] Porter K., Kennedy R., Bachman R., 2007. Creating fragility functions for performancebased earthquake engineering. Earthq. Spectra 23 (2), 471-489. https://doi.org/10.1193/1.2720892.

[25] Seismic hazard atlas for the design earthquake of the Philippines (with Philippine institute of volcanology and seismology (DOST - phivolcs)). Department of Science and Technology - Philippine Institute of Volcanology and Seismology (DOST PHIVOLCS), 2024.

[26] Sengara I.W., Irsyam M., Sidi I.D., Mulia A., Asrurifak M., Hutabarat D., Partono W., 2020. New 2019 risk-targeted ground motions for spectral design criteria in Indonesian seismic building code. E3S Web of Conferences 156, 03010. https://doi.org/10.1051/e3sconf/202015603010.

[27] Shin D.H., Kim H.-J., 2015. Domestic seismic design maps based on risk-targeted Maximum- considered earthquakes. Journal of the Earthquake Engineering Society of Korea 19 (3), 93-102. https://doi.org/10.5000/EESK.2015.19.3.093.

[28] Shinozuka M., Feng M.Q., Lee J., Naganuma T., 2000. Statistical analysis of fragility curves. J. Eng. Mech. 126 (12), 1224-1231. https://doi.org/10.1061/(ASCE)07339399(2000)126:12(1224.

[29] Silva V., Crowley H., Bazzurro P., 2016. Exploring risk-targeted hazard maps for Europe. Earthq. Spectra 32 (2). https://doi.org/10.1193/112514eqs198m.Article2.

[30] Spillatura A., Vamvatsikos D., Kohrangi M., Bazzurro P., 2023. Harmonizing seismic performance via risk targeted spectra: state of the art, dependencies, and implementation proposals. Earthq. Eng. Struct. Dynam. 52 (13), 4277-4299. https://doi.org/10.1002/eqe.3941.

[31] Taherian A.R., Kalantari A., 2019. Risk-targeted seismic design maps for Iran. J. Seismol. 23 (6), 1299-1311. https://doi.org/10.1007/s10950-019-09867-6.

[32] Talebi M., Zare M., Noroozinejad Farsangi E., Soghrat M.R., Maleki V., Esmaeili S., 2021. Development of risk-targeted seismic hazard maps for the Iranian Plateau. Soil Dynam. Earthq. Eng. 141, 106506. https://doi.org/10.1016/j.soildyn.2020.106506.

[33] Uniform Building Code (with International Conference of Building Officials), 1997. International Conference of Building Officials.

[34] Vamvatsikos D., 2013. Derivation of new SAC/FEMA performance evaluation solutions with second-order hazard approximation. Earthq. Eng. Struct. Dynam. 42 (8), 1171-1188. https://doi.org/10.1002/eqe.2265.