The Seismic Hazards Posed by New Mapped Offshore Segments of the Ranong and Khlong Marui Faults

Open Access
Ramirez, Haley M
Graduate Program:
Master of Science
Document Type:
Master Thesis
Date of Defense:
September 14, 2018
Committee Members:
  • Kevin Patrick Furlong, Thesis Advisor
  • Sridhar Anandakrishnan, Committee Member
  • Donald Myron Fisher, Committee Member
  • Intraplate
  • Thailand
  • Strike - Slip
The Ranong and Khlong Marui Faults in Southern Thailand have clear surface expressions but their southern offshore extents have not been previously mapped. The lack of information about these faults makes it difficult to evaluate the seismic hazard they pose to Southern Thailand. This study maps the offshore extent of these faults using a marine seismic reflection survey. We model their potential earthquake activity to better understand the seismic hazard they pose to Southern Thailand. We mapped four active offshore faults approximately along strike with the onshore Ranong and Khlong Marui Faults. We connected these offshore faults with the onshore faults to estimate the full potential extent of the Ranong and Khlong Marui Faults. We also estimated the maximum earthquake magnitudes that could occur on these faults using an empirical scaling equation that relates fault length and earthquake size (Wesnousky, 2008). The maximum earthquake magnitudes for the offshore portions of the Ranong and Khlong Marui Faults range from Mw 6.55 to 6.88. The full (offshore and onshore segments) portion of the Ranong Fault could host a Mw=7.85 earthquake. Similarly, the full portion of the Khlong Marui Fault could host a Mw=7.51 earthquake. In order to assess the possible consequences of such earthquakes, we modeled stress changes and strong ground motion from scenario earthquakes on each of these faults. We used Coulomb stress modeling to address how an earthquake on these faults could increase the seismicity risk in the region. An earthquake on the offshore mapped faults could increase the Coulomb stress and possible risk of seismicity on the longer onshore portions of the Ranong and Khlong Marui Faults by triggering an earthquake on the faults along strike. We use ShakeMaps modeling (USGS) to quantify peak ground acceleration and shaking intensity from a scenario earthquake. We find that the offshore fault segments alone could only cause a ground shaking intensity of V to VI near the tourist city of Phuket. However, if these offshore segments are connected to the onshore Ranong or Khlong Marui Faults, they could cause a shaking intensity of VIII in the cities nearest to the faults. The cities of Kapong and Ranong could experience peak ground acceleration of more than 0.50g. An event of this magnitude could be damaging to Southern Thailand.