Earthquake behaviors in Source Time functions: energetic onset of earthquakes and biases from over-simplifying the source pulse

Marine A. Denolle, & Philippe J. Danré

Published August 6, 2018, SCEC Contribution #8284, 2018 SCEC Annual Meeting Poster #213 (PDF)

Global databases of earthquake source time functions (STFs) provide tremendous opportunities to explore the temporal evolution of the source. We use two such databases (SCARDEC Vallee 2011,2016 and USGS Hayes 2017), to extract information about earthquake behaviors from the shape of the STF. First, it is common to focus on the amplitude Fourier spectrum, provided an accurate and/or empirical treatment of wave propagation, and to simplify the source spectrum through smooth spectral shapes (Brune-like, Boatwright-like, Haskell-like). In particular, the attribution of a best-fit corner frequency to a source duration is usually qualitative and assumed magnitude-independent. Here, we show that the complexity in spectral shapes, which grows with earthquake magnitude (Danre et al 2018), biases the estimate of a corner frequency such that the relation between true pulse duration and modeled corner frequency depends on earthquake magnitude. This suggests that the interpretation of corner frequency in terms of earthquake stress drop may introduce a scaling bias. Second, we explore the temporal evolution of the moment-rate functions, the seismic power that we derive from moment accelerations, and the temporal evolution of the ratio of both that is a time-dependent scaled energy. We find that earthquake onset contains most of the seismic radiation and that radiation productivity is mostly contained within 10% of the total duration of the source. This suggests that earthquake development is more energetic and abrupt than earthquake arrest.

Key Words
source time function, nucleation, corner frequency, stress drop, earthquake scaling

Citation
Denolle, M. A., & Danré, P. J. (2018, 08). Earthquake behaviors in Source Time functions: energetic onset of earthquakes and biases from over-simplifying the source pulse. Poster Presentation at 2018 SCEC Annual Meeting.

Related Projects & Working Groups
Fault and Rupture Mechanics (FARM)