EFFECT OF FINITE THICKNESS OF SCATTERING LAYER ON CODA Q OF LOCAL EARTHQUAKES

Abstract

Theories based on the assumption of an infinite medium show that the coda attenuation factor, Q-1c, of local earthquakes should be very close to the intrinsic Q-1i, whereas many observations show that Q-1c is close to the totalQ-1 (Q-1t). This paper shows by numerical modeling that Q-1c depends on the thickness of the scattering layer. For source-receiver coincidence, if the thickness is greater than a half of the mean free path, Q-1c lies between Q-1i and Q-1t. However, when the thickness is less, Q-1c may be higher than Q-1t. In addition,Q-1c depends on the epicentral distance. The thinner the layer, the faster the change with distance in Q-1c. For an unbounded scattering medium Q-1c is even lower than Q-1i at long epicentral distances.