Revised earthquake sources along Manila Trench for tsunami hazard assessment in the South China Sea

Abstract

Abstract. Seismogenic tsunami hazard assessments are highly dependent on the reliability of earthquake source models. Here in a study of the Manila subduction zone (MSZ) system, we combine the geological characteristics of the subducting plate, the geometry, and coupling state of the subduction interface to propose a series of fault rupture scenarios. We divide the subduction zone into three rupture segments: 14° N–16° N, 16° N–19° N and 19° N–21.7° N inferred from geological structures associated with the down-going Sunda plate. Each of these segments is capable of generating earthquakes of magnitude between Mw 8.5+ and Mw 9+, assuming a-1000-year seismic return period as suggested by previous studies. The most poorly constrained segment of the MSZ lies between 19° N–21.7° N, and here we use both local geological structures and characteristics of other subduction zone earthquakes around the world, to investigate the potential rupture characteristics of this segment. We consider multiple rupture modes for tsunamigenic-earthquake type and megathrust-splay fault earthquakes. These rupture models facilitate an improved understanding of the potential tsunami hazard in the South China Sea (SCS). Hydrodynamic simulations demonstrate that coastlines surrounded the SCS could be devastated by tsunami waves up to 10-m if large megathrust earthquakes occur in these segments. The regions most prone to these hazards include west Luzon of Philippines, southern Taiwan, the southeastern China, central Vietnam and the Palawan Island.

Probabilistic Tsunami Hazard Assessment (PTHA) for Southeast Coast of Chinese Mainland and Taiwan Island

“…(2016) showed that the occurrence of great earthquakes of M w 8.8–9.2 in the Manila Trench is plausible. It was further supported by (Qiu et al., 2019) that the Manila Trench is capable of generating M w 8.5+ earthquakes with a return period of 1,000 years.…”

Tsunamigenic Potential of the Baiyun Slide Complex in the South China Sea

“…However, the chances of preserving tsunami deposits greatly decrease due to intense human activities, for example, land reclamation, urban development in coastlines of the mainland. So far, all the sites which have reported geological evidence of possible tsunamis in SCS are located in relatively remote islands (Qiu et al, ), including Dongdao Island (Sun et al, ), Yongshu Island (Yu et al, ), Badoc Island near Luzon (Ramos et al, ) and Nanao Island in southern Chinese coastline (Yang et al, ). Based on the combined information of numerical results, geological setting and the available geological studies, we would suggest that the islands located in the offshore area of southern China have the highest chance for such evidence being found.…”

“…Compared with the bathymetry on the eastern and western sides alongshore, the seafloor bathymetry perpendicular to the coastline in front of the PRE is relatively high, which forms a hump, slows down wave propagation and leads to shoaling of the tsunami waves. (5) In terms of tsunami arrival time, when comparing with the tsunami waves generated by megathrust earthquakes from the Manila subduction zone (Qiu et al, ), tsunami waves generated by the studied landslides arrive ~1 hr earlier at coastlines in southern China and central Vietnam and ~0.5 hr later at coastlines in Taiwan and Philippines. (6) Nonlinearity has a considerable effect on the coasts with wide continental shelf, especially in front of the PRE region, and has negligible effect on coasts with a narrow continental shelf, for instance, western Philippines, central Vietnam, and Southern Taiwan.…”