Fast moment acceleration in the development phase of an earthquake derived from a large catalog of Source Time Functions
Julien Renou, & Martin ValléePublished August 7, 2018, SCEC Contribution #8304, 2018 SCEC Annual Meeting Poster #074
The earthquake source physics giving rise to events of very different magnitudes remains debated. Features in the initiation phase carrying information on the final magnitude have been proposed. Conversely, in the cascade model, the rupture grows in a magnitude-independent way, implying that the final seismic moment $M_0$ is controlled by the earthquake duration. The characteristics of the accelerating phase of the rupture process (hereafter mentioned as ``development phase'') provides insights on these competing hypotheses and can help to constrain the rupture dynamics.
Our study aims at observing the development phase using the SCARDEC database, a global catalog containing more than 3000 Source Time Functions (STFs) of earthquakes with magnitude $M_w > 5.7$. The method consists in computing the STFs slope, i.e. the moment acceleration, at several prescribed moment rates. In order to ensure that the chosen moment rates intersect the development phase of the STF, we select in all STFs the window in which the signal is both not too low and not too close from the peak. This approach does not use any rupture time information, which is interesting as (1) the exact hypocentral time can be uncertain and (2) the main rupture expansion can be delayed compared to origin time. Thus, even if the times at which rupture strongly develops vary a lot, the method always isolates the development phase.
First results do not exhibit variations of the slope with magnitude. However, our method clearly points out that slope values fastly increase with the moment rate, which leads to a moment in the development phase growing quicker than cubically with time. The existence of such a local fast-growing phase, together with other time windows of the STF where the rupture is less efficient, are qualitatively consistent with the classical scaling $M_{0} \propto T^3$ observed for the whole rupture duration $T$. We finally create a synthetic STF catalog integrating the properties of the development phase and reproducing the real SCARDEC catalog diversity. Consistently with previous studies, our median of synthetic STFs tends to have a linear growth. As none of the individual synthetic STFs develop linearly, this observation is understood to result from the large diversity of the STFs shapes, and its physical interpretation has therefore to be done with care.
Citation
Renou, J., & Vallée, M. (2018, 08). Fast moment acceleration in the development phase of an earthquake derived from a large catalog of Source Time Functions. Poster Presentation at 2018 SCEC Annual Meeting.
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Seismology
