The Initiation of Submarine Debris Flow after 2006 Pingtung Earthquake Offshore Southwestern Taiwan

Abstract:

On 26－27 December 2006, a series of submarine cables were damaged offshore southwestern Taiwan from Gaoping Slope to the northern terminus of the Manila Trench. The cable breakages were caused by gravity flows which triggered by the Pingtung earthquake doublet occurred on 26 December 2006 at 20:26 (21.9°N, 120.6°E; M_L 7.0) and 20:34 (21.97°N, 120.42°E; M_L 7.0) offshore of Fangliao Twonship and meanwhile the local fishermen reported disturbed waters at the head of Fangliao submarine canyon. Although many researchers conjectured the disturbed waters may cause by the eruption of submarine volcanoes which has been widely discovered off the southwestern Taiwan, the actual mechanism is still unclear. In previous studies, a series of faults, liquefaction strata, pockmarks and acoustically transparent sediments with doming structures were observed at the head of Fanliao submarine canyon and may highly related to the submarine groundwater discharge off southwestern Taiwan. Recently, further multi-beam surveys were conducted at the east of Fangliao submarine canyon head and the result shows large area of seafloor subsidence after Pingtung Earthquake. The area of subsidence is over 60 km² with maximum depth around 5 meters. The north end of the subsidence is connected to the Fangliao submarine canyon where the first cable was failed (CH-US CN-W2-1: 22°13.287’N, 120°33.722’E) after Pingtung Earthquake. All the evidences point out the large earthquake might triggered liquefaction process and generated large debris flow and swept the submarine cables away from the Fangliao submarine canyon head to the abyss.