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Coseismic and potential earlier afterslip distribution of the 2009 Mw 6.3 L’Aquila, Italy earthquake

Tomoko E. Yano, Guangfu Shao, Qiming Liu, Chen Ji, & Ralph J. Archuleta

Published 2014, SCEC Contribution #1781

In view of significant discrepancy between the slip models of the 2009 April 6 L’Aquila, (Italy) earthquake based on seismic waveforms or geodetic data, a new inversion strategy is proposed to constrain the coseismic rupture model and early post-seismic afterslip model of this earthquake. Both models were jointly inverted simultaneously from the near-source strong ground motion recordings, teleseismic P waves, long-period Rayleigh waves, GPS displacement vectors and InSAR line-of-sight displacement image. The deformations are mapped onto the fault with strike 140◦ and dip 50◦ to the southwest. The coseismic period here represents the first 10 s after the rupture initiation, when over 99 per cent of our total seismic moment (3.07 × 1018 Nm) is already released in our preferred coseismic model. Most coseismic slip occurs in a small rupture area of approximately 16 km along strike and in a depth range of 3–10 km. The average slip is 0.45 m; peak slip reaches about 0.90 m. Our result reveals that L’Aquila rupture has a lag of 0.6 s before it first propagates updip to break an asperity equivalent to an Mw 5.7. And then the rupture propagates along strike to break a large patch located about 8.0 km along strike and 4.0 km updip from the hypocentre. The weighted average of the rise time and slip velocity are 0.71 s and 0.77 m s−1, respectively. Our estimate of radiated seismic energy is 1.67 × 1013 J, yielding an energy to seismic moment ratio of 0.55 × 10−5, considerably smaller than the global average for shallow earthquakes. The early post-seismic period here represents the time window from 10 s to about first day. During this period, our preferred post-seismic model has an accumulated seismic moment of 6.0 × 1017 Nm, equivalent to an Mw of 5.8. The afterslip distribution features two separated high slip fault patches, locating either near the hypocentre or the region with peak coseismic slip. Their locations only partially overlap with the fault patches with significant afterslip after the first day. In particular, the slip distribution of the shallower patch is quantitatively consistent with the Amoruso and Crescentini’ diffusive afterslip model. Therefore, the coseismic rupture of the 2009 L’Aquila earthquake was following by a slow-slip event with significant moment release in first hour.

Yano, T. E., Shao, G., Liu, Q., Ji, C., & Archuleta, R. J. (2014). Coseismic and potential earlier afterslip distribution of the 2009 Mw 6.3 L’Aquila, Italy earthquake. Geophysical Journal International, 199, 23-40. doi: 10.1093/gji/ggu241.