HR: 1330h
AN: S42C-0191    [PDF]
TI: The Magnitude and Energy of Large Earthquakes
AU: * Purcaru, G
EM: purcaru@geophysik.uni-frankfurt.de
AF: Institute of Meteorology & Geophysics, Univ. of Frankfurt/M, Feldbergstr. 47, Frankfurt/Main, 60323 Germany
AB: Several magnitudes were introduced to quantify large earthquakes better and more comprehensive than $M_s$: $M_w$ (moment magnitude; Kanamori, 1977), $M_E$ (strain energy magnitude; Purcaru and Berckhemer, 1978), $M_t$ (tsunami magnitude; Abe, 1979), $M_m$ (mantle magnitude; Okal and Talandier, 1985), $M_e$ (seismic energy magnitude; Choy and Boatwright, 1995). Although these magnitudes are still subject to different uncertainties, various kinds of earthquakes can now be better understood in terms or combinations of them. They can also be viewd as mappings of basic source parameters: seismic moment, strain energy, seismic energy, stress drop, under certain assumptions or constraints. We studied a set of about 90 large earthquakes (shallow and deeper) occurred in different tectonic regimes, with more reliable source parameters, and compared them in terms of the above magnitudes. We found large differences between the strain energy (mapped to $M_E$) and seismic energy (mapped to $M_e$), and between $M_E$ of events with about the same $M_w$. This confirms that no 1-to-1 correspondence exists between these magnitudes (Purcaru, 2002). One major cause of differences for "normal" earthquakes is the level of the stress drop over asperities which release and partition the strain energy. We quantify the energetic balance of earthquakes in terms of strain energy $E_{st}$ and its components (fracture ($E_g$), friction ($E_f$) and seismic ($E_s$) energy) using an extended Hamilton's principle. The earthquakes are thrust-interplate, strike slip, shallow in-slab, slow/tsunami, deep and continental. The (scaled) strain energy equation we derived is: $E_{st}/M_0 = (1+e(g,s))(E_s/M_0)$, $e(g,s) = E_g/E_s$, assuming complete stress drop, using the (static) stress drop variability, and that $E_{st}$ and $E_s$ are not in a 1-to-1 correspondence. With all uncertainties, our analysis reveal, for a given seismic moment, a large variation of earthquakes in terms of energies, even in the same seismic region. In view of these, for further understanding of earthquakes behaviour we introduce energy classes, and present first results.
DE: 7209 Earthquake dynamics and mechanics
DE: 7215 Earthquake parameters
DE: 7223 Seismic hazard assessment and prediction
DE: 7260 Theory and modeling
SC: Seismology [S]
MN: 2003 Fall Meeting