Determination of earthquake energy release in the Eastern Mediterranean region

Seismic energy radiated by earthquakes in the Eastern Mediterranean region is estimated using the short-period (50 samples per second) seismic recordings made by the Israel Seismic Network during 1990-1997. Our data set is the whole S-wave window (from S_n until L_g falls to less than twice the noise level) from 133 earthquakes with a high signal-to-noise ratio. We obtained the attenuation function (1.850 ± 0.005) log R + (0.00460 + 0.00005)R log e + 0.05, where the distance range is 50 ≤ R ≤ 1500 km. We tested the dependence of the attenuation function on the azimuth and the distance. Despite the different propagation paths of the waves travelling through the continental crust of the Arabian Shield to the east or the intermediate crust of the Mediterranean Sea to the west, we show that from a statistical point of view the attenuation functions are similar. The energy estimation involves time-domain integration of the squared ground-motion velocity, assuming that the attenuation is known, following the method of Kanamori et al. (1993). For the magnitude range 3.0≤m_B≤6.2 (magnitude determined by the National Earthquake Information Service, NEIS), we obtained the magnitude-energy relationship log E₀ = (2.09 ± 0.10)m_B + (8.86 ± 0.42). Comparison of the seismic energy and the seismic moment suggests that E ∝ M₀^0.19 and that Orowan's stress drop increases as M₀^0.19. A refinement of the results is expected with the application of the method of Mayeda & Walter (1996) for energy estimation from coda envelopes using a large data set of broad-band observations.