Radiated seismic energy and source damage evolution from the analysis of simulated dynamic rupture and far-field seismograms. Issue 3 (26th July 2022) - Kurzon, Ittai
SUMMARY: We present results on radiated seismic energy during simulations of dynamic ruptures in a continuum damage-breakage rheological model incorporating evolution of damage within the seismic source region. The simulations vary in their initial damage zone width and rate of damage diffusion with parameter values constrained by observational data. The radiated energy recorded at various positions around the source is used to calculate seismic potency and moment. We also calculate the normalized radiated energy from the source, in a way that allows comparing between results of different simulations and highlighting aspects related to the dilatational motion during rupture. The results show that at high-frequencies, beyond the dominant frequency of the source ($( {f > 3{f}_d} )$, the damage process produces an additional burst of energy mainly in the P waves. This eccess of high-frequency energy is observed by comparing the radiated energy to a standard Brune's model with a decay slope of the radiated energy of n = 2. While the S waves show good agreement with the n = 2 slope, the P waves have a milder slope of n = 1.75 or less depending on the damage evolution at the source. In the used damage-breakage rheology, the rate of damage diffusivity governs the damage evolution perpendicular to the rupture direction and dynamic changes of the damage zone width. For increasing values of damage diffusivity, dilatational energy becomes more prominent during rupture, producing a high-frequency dilatational signature within the radiation pattern. The high-frequency radiation pattern of the P waves includes two main lobes perpendicular to the rupture direction, reflecting high-rate local tensile cracking during the overall shear rupture process. Analysing the possible existence and properties of such high-frequency radiation pattern in observed P waves could provide important information on earthquake source processes.