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Title: Study of Tsunamigenesis of earthquakes
Authors: KARMA
Keywords: Tsunamigenesis, Tsunamigenic, Source Parameters, Tsunami Prediction, Tsunami warning, Frequency Analysis
Issue Date: 17-Aug-2009
Citation: KARMA (2009-08-17). Study of Tsunamigenesis of earthquakes. ScholarBank@NUS Repository.
Abstract: Tsunamis are one of the most destructive forces in nature and it can cause much loss of life and property damage. Majority of tsunamis are generated by earthquake events. Some earthquakes produce very severe tsunamis, e.g. the December 2004 Aceh earthquake while others generate only minor wave tsunami, e.g. the March 2005 Nias earthquake. Thus, the study of tsunamigenesis of earthquakes, i.e., whether an earthquake will generate significant tsunami, is critical for early tsunami warning. The destruction and loss of life from 2004 tsunami event was so catastrophic that the whole world stood in shock at the sheer power of nature. The mechanism and generation of tsunami is very complex, thus the current method of tsunami prediction is inadequate as evident from more than 50% false warnings issued by Pacific Tsunami Warning Center (PTWC).

Additional information on the earthquake source mechanism could enhance tsunami predictability. Thus, the first objective of this research is the identification of the key features of tsunamigenic earthquakes for development of suitable methodologies for timely tsunami prediction. The second objective is the development of near real-time tsunami forecasting techniques with particular focus on Southeast Asia. The ultimate objective of this research is to contribute to the development of an advanced tsunami warning system.

Spectral Analyses (FFT and CWT) were conducted on seismograms of pairs of earthquakes (i.e. one tsunamigenic and the other non-tsunamigenic) that occurred in close proximity and in similar tectonic zones with comparable magnitudes and epicenter distance to determine tsunamigenesis. The results consistently showed that tsunamigenic earthquakes are depleted in high frequency (>0.1 Hz) seismic radiations compared to non-tsunamigenic earthquakes. This finding is also directly related to the possible fault rupture mechanism responsible for the tsunami generation: slow rupture speed.

Next, the Empirical Mode Decomposition (EMD) technique was used to decompose the seismic signals into different frequency components and analyzed. The results showed that tsunami earthquake is depleted in high frequency (>0.1 Hz) energy but enriched in the longer period (>100 s) waves. The tsunami earthquake also has longer corner period (indicating larger rupture) compared to the ordinary earthquake of similar magnitude.

Both the Spectral and EMD analyses involve time delay since the surface waves, were mainly used in the analyses. Thus, a faster Rupture Analysis technique based on analysis of high-frequency (2-4 Hz) P waves was investigated. The results showed that all the tsunamigenic earthquakes analyzed exhibited rupture duration exceeding 100 s while non-tsunamigenic earthquakes showed less than a minute.

In addition to tsunami prediction, a data-driven technique was developed in collaboration with other researchers in this project (Tkalich et al., 2008) to forecast the arrival time and wave heights of the tsunami after a tsunamigenic earthquake has occurred. With this collaborative effort, reasonable forecasting results could be obtained in seconds corresponding to any particular sets of input source parameters.

Finally, since the tsunamigenic potential of an earthquake was found to be related to its seismic moment, an effort was made to compute the earthquake source parameters using moment tensor inversion near b real timeb . The results of moment magnitude and focal mechanism showed good agreement with those from Harvard CMT solutions.

The best way to minimize destruction from an earthquake is to have practical measures in place before the large earthquake hits, not after. Thus, some of research findings were incorporated in the early tsunami warning system in Singapore while others still remain at the research stage.
Appears in Collections:Ph.D Theses (Open)

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