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Monday, 11 June 2018 00:00

A new underlying mechanism in deadly 7.1R quake in Taiwan in 1906 has been uncovered

The earthquake was one of the deadliest to ever strike the country

The earthquake was one of the deadliest to ever strike the country

The 1906 Meishan earthquake, named after the village near where it occurred, is the third-deadliest quake in Taiwan's recorded history, claiming around 1,260 lives. It had a surface wave magnitude of 6.8 and a focal depth of 6 km (4 mi), while it was related to the Meishan fault, which had an about 12.5 km right‐lateral surface rupture orientated in an east–west direction. Considering the short surface rupture with respect to the magnitude of the earthquake, combined with the fact that the north–south pattern of damage is not consistent with the strike of the surface rupture, researchers had doubts regarding the exact mechanism of the earthquake.

Taking these inconsistencies into account, researchers from Taiwan’s National Central University, decided to reexamine the historical records of the earthquake. They used the original seismogram recordings from three seismic stations in the country (Taipei, Taichung, and Tainan), which were archived at the Earthquake Research Institute of Tokyo University, along with historical literature collected with the help of Taiwan's Central Weather Bureau. This way, they managed to create new artificial (because of the difficulties in accounting for unknown instrument responses and in digitizing the historical records) waveform simulations for the quake and evaluated several models of how the fault might have ruptured. Finally, they uncovered a discrepancy between the first motions of P-waves and S-waves (the first and second waves detected by a seismograph in the event of an earthquake), suggesting that the mechanism might not have been a pure strike-slip rupture, says Kuo‐Fong Ma, from the Earthquake‐Disaster & Risk Evaluation and Management (E‐DREaM) Center, National Central University, and the study’s lead author. Trying to find an alternative fault motion in the region that could better explain the data, the scientists concluded that the preferred mechanism would be a thrust fault oriented in a northeast-southwest direction, with a small right-lateral component. ‘Rupture along this type of thrust fault is more consistent with the level of shaking intensity and the pattern of aftershocks seen after the 1906 earthquake’, Ma and colleagues said. The new mechanism unveiled, provides a better fit for the fault rupture expected from the magnitude 7.1. earthquake, as well as a better fit for the distribution of recorded damage and aftershocks.

The study’s outcome, which was recently published in GeoScienceWorld, highlights the importance of historical recordings in resolving the earthquake mechanism in a complex fault system, as ‘it is important for seismologists to provide better information for seismic hazard assessment,’ said Kuo-Fong Ma. The finding might also encourage others to use historical records in tectonically active countries to ‘explore the full fault system rather than a single fault segment for seismic hazard evaluation’ she added.

Source: Seismological Society of America

Read 326 times Last modified on Monday, 11 June 2018 15:37

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