Venkataraman, Anupama (2002) Investigating the mechanics of earthquakes using macroscopic seismic parameters. Dissertation (Ph.D.), California Institute of Technology. http://resolver.caltech.edu/CaltechETD:etd-06132002-094224
To understand the physics of earthquake rupture mechanics, we have to relate seismologically observable parameters to the dynamics of faulting. One of the key seismological parameters that will help us achieve this objective is radiated energy. In this work, we develop a new method of estimating radiated energy from regional data using an empirical Green's functions; we also modify existing methods of estimating radiated energy from teleseismic data by improving the corrections applied to the observed seismic data for attenuation and directivity effects.
We compute teleseismic estimates of radiated energy for 23 large subduction zone earthquakes recorded between 1992 and 2001; most of these earthquakes have a magnitude, Mw > 7.5, but we also include some smaller (Mw~6.5) well-studied subduction zone earthquakes and 6 crustal earthquakes. We compile the static stress drop estimates for these 29 earthquakes from published literature. We then determine radiation efficiency of these earthquakes using a stress relaxation model that relates measurable and macroscopic seismological parameters to the physical processes on the fault zone via fracture energy. We also determine the rupture velocity of these earthquakes from published literature. A comparison of radiation efficiencies and rupture velocities of these earthquakes with the expected theoreticial values for different modes of crack propagation validates the use of the stress relaxation model to understand earthquake rupture mechanics.
From our calculations, we observe that most earthquakes have radiation efficiencies between 0.25 and 1 and are hence efficient in generating seismic waves, but tsunami earthquakes and two deep earthquakes, the 1994 deep earthquake that occurred in Bolivia and the 1999 Russia-China border earthquake, have very small radiation efficiencies (<0.25) and hence dissipate a large amount of energy on the fault plane. We suggest that the difference in the radiation efficiencies of the different types of earthquakes could be due to fundamental differences in the rupture mechanics of different events. In case of deep events, the energy is probably dissipated in thermal processes on the fault zone, while it is possible that the morphology of the trench causes branching and bifurcation of rupture resulting in the large energy dissipation during the rupture process of tsunami earthquakes.
|Item Type:||Thesis (Dissertation (Ph.D.))|
|Subject Keywords:||deconvolution; empirical Green's function method; fracture energy; macroscopic seismic paramaters; partitioning of energy in earthquakes; radiated seismic energy; radiation efficiency; rupture velocity; static stress drop; subduction zone; tsunami earthquakes|
|Degree Grantor:||California Institute of Technology|
|Division:||Geological and Planetary Sciences|
|Thesis Availability:||Public (worldwide access)|
|Defense Date:||29 April 2002|
|Author Email:||anupama (AT) gps.caltech.edu|
|Default Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Imported from ETD-db|
|Deposited On:||17 Jun 2002|
|Last Modified:||26 Dec 2012 02:52|
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