Complexity of the Mw 6.3 2009 L'Aquila (central Italy) earthquake: 2. Broadband strong motion modeling

Abstract

[1] Near-fault strong-ground motions (0.1-10 Hz) recorded during the Mw 6.3 2009 L'Aquila earthquake exhibit great spatial variability. Modeling the observed seismograms allows linking distinct features of the observed wavefield to particular source and propagation effects and provides insights on strong motion complexity from this moderate magnitude event. We utilize a hybrid integral-composite approach based on a k-square kinematic rupture model, combining low-frequency coherent and high-frequency incoherent source radiation and providing omega-squared source spectral decay. Several source model features, proven to be stable by means of an uncertainty analysis in the preceding low-frequency (<0.2 Hz) multiple finite-extent source inversion (Paper 1), were constrained. Synthetic Green's functions are calculated in a 1D-layered crustal model including 1D soil profiles to account for site-specific response (where available). The results show that although the local site effects improve the modeling, the spatial broadband ground-motion variability is to large extent controlled by the rupture kinematics. The modeling thus confirms and further constraints the source model features, including the position and slip amount of the two main asperities, the largest asperity time delay and the rupture velocity distribution on the fault. Furthermore, we demonstrate that the crossover frequency dividing the coherent and incoherent wavefield, often considered independent on the station position, has to be variable in order to adequately reproduce both near and far station recordings. This suggests that the incoherency of the radiated wavefield is controlled by the wave-propagation phenomena and/or the initial updip rupture propagation was very smooth (coherent) up to relatively high frequencies (>2 Hz).

The 3D numerical simulation of near-source ground motion during the Marsica earthquake, central Italy, 100 years later

“…It is characterized by five horizontal and parallel layers resting on a half-space at a depth of 20 km. In particular the V S values of the shallow layers have been reduced with respect to those of [14], in agreement with the site investigations [15], in order to decrease the basin-to-rock impedance ratio. The properties of each layer are shown in Table 1.…”

“…A crustal model is adopted based on [14]. It is characterized by five horizontal and parallel layers resting on a half-space at a depth of 20 km.…”

Fault Segmentation as Constraint to the Occurrence of the Main Shocks of the 2016 Central Italy Seismic Sequence

“…The waveforms were downsampled to the time step of 0.4 s. In order to strengthen the role of stations located further away from the fault, we increase their weight by a factor of 2 with respect to stations located above the fault. Synthetic Green's functions were calculated by the discrete wave number and matrix methods (Bouchon, ; Coutant, ; Kennett & Kerry, ) for a 1‐D velocity model adopted from Gallovič and Zahradník () and Ameri, Gallovic, and Pacor (), for the low‐frequency and broadband modeling of the 2009 L'Aquila earthquake, respectively. We fix the parameter controlling the smoothing strength (Gallovič et al, ) at a value providing a good balance between rupture complexity (minimum ghost features) and data fit and adopt this value for the three events.…”

Spectral models for ground motion prediction in the L'Aquila region (central Italy): evidence for stress-drop dependence on magnitude and depth

“…The adopted velocitydepth function is the 1-D model by Bianchi et al (2010), obtained from receiver function analyses and used by Ameri et al (2012) to simulate the recorded ground motions of L'Aquila main shock. The estimated stress drops have a mean equal to 2.6 MPa, with the bulk of the observations ranging between 1 and 5 MPa (Fig.…”