New formulation reduces the scatter of earthquake stress drop estimation

Stress-drop is the overall reduction of average stress due to energy release during an earthquake, and should reflect geometrical, rheological and dynamic properties of the seismic source. Stress-drop values, estimated using seismological data, vary over four orders of magnitudes making the stress-drop an enigmatic parameter. There have been many efforts to reduce the stress-drop scatter, and to perceive better understanding of the factors controlling its variability. These efforts focused mainly on observational aspects, in which source properties such as, corner-frequency and seismic moment, were measured, considering site, path and additional source properties. Standard cubic power-law relation between corner-frequency of radiated waves and stress-drop, with a constant coefficient K, is and additional reason to its significant scatter. We provide a new formulation, applying a strain-drop dependent K; by that leading to a significant reduction of the relation of stress-drop to corner-frequency, down to a power-law of 3/4. Results based on a wide range of theoretical, laboratory and observational measurements demonstrate that the new formulation significantly narrows the three to four orders of magnitude of scatter, to about one order of magnitude around a value of 10MPa. The more converged range of stress-drop values, obtained by the suggested new formulation, may be used to support those who argue for self-similarity of earthquakes. In summary, the impact of the uncertainties of the source properties, seismic moment, M₀, seismic potency, P₀, and corner frequency, f_C, on the value of stress-drop is not as dramatic as so many studies argued before. Furthermore, as we demonstrate, the reduction of scatter does not eliminate internal trends, controlled by geometrical, rheological and dynamical properties at the source.