HR: 1340h
AN: S13D-1091    [Abstracts]
TI: The Strain Energy, Seismic Moment and Magnitudes of Large Earthquakes
AU: * Purcaru, G
EM: purcaru@geophysik.uni-frankfurt.de
AF: Inst. of Meteorology & Geophysics, Univ. of Frankfurt, Feldbergstr. 47, Frankfurt/Main, D-60323 Germany
AB: The strain energy $E_{st}$, as potential energy, released by an earthquake and the seismic moment $M_o$ are two fundamental physical earthquake parameters. The earthquake rupture process ``represents'' the release of the accumulated $E_{st}$. The moment $M_o$, first obtained in 1966 by Aki, revolutioned the quantification of earthquake size and led to the elimination of the limitations of the conventional magnitudes (originally ML, Richter, 1930) mb, Ms, m, MGR. Both $M_o$ and $E_{st}$, not in a 1-to-1 correspondence, are uniform measures of the size, although $E_{st}$ is presently less accurate than $M_o$. Est is partitioned in seismic- ($E_s$), fracture- ($E_g$) and frictional-energy $E_f$, and $E_f$ is lost as frictional heat energy. The available $E_{st} = E_s + E_g$ (Aki and Richards (1980), Kostrov and Das, (1988) for fundamentals on $M_o$ and $E_{st}$). Related to $M_o$, $E_{st}$ and $E_s$, several modern magnitudes were defined under various assumptions: the moment magnitude $M_w$ (Kanamori, 1977), strain energy magnitude $M_E$ (Purcaru and Berckhemer, 1978), tsunami magnitude $M_t$ (Abe, 1979), mantle magnitude $M_m$ (Okal and Talandier, 1987), seismic energy magnitude $M_e$ (Choy and Boatright, 1995, Yanovskaya et al, 1996), body-wave magnitude $M_{pw}$ (Tsuboi et al, 1998). The available $E_{st} = (1/2\mu)\Delta\sigma M_o$, $\, \Delta\sigma$~=~average stress drop, and M$_E$ is % \[M_E = 2/3(\log M_o + \log(\Delta\sigma/\mu)-12.1)\, ,\] % and $\log E_{st} = 11.8 + 1.5 M_E$. The estimation of $E_{st}$ was modified to include $M_o$, $\Delta$ and $\mu$ of predominant high slip zones (asperities) to account for multiple events (Purcaru, 1997): % \[E_{st} = \frac{1}{2} \sum_i {\frac{1}{\mu_i} M_{o,i} \Delta\sigma_i} \, , \hspace{0.8cm} \sum_i M_{o,i} = M_o \] % We derived the energy balance of $E_{st}$, $E_s$ and $E_g$ as: % \[ E_{st}/M_o = (1+e(g,s)) E_s/M_o \, , \hspace{0.8cm} e(g,s) = E_g/E_s \] % We analyzed a set of about 90 large earthquakes and found that, depending on the goal these magnitudes quantify differently the rupture process, thus providing complementary means of earthquake characterization. Results for some classes of large earthquakes are discussed.
DE: 7260 Theory and modeling
DE: 7209 Earthquake dynamics and mechanics
DE: 7215 Earthquake parameters
SC: Seismology [S]
MN: 2004 AGU Fall Meeting