The Effectiveness of a Distant Accelerometer Array to Compute Seismic Source Parameters: The April 2009 L'Aquila Earthquake Case History

Abstract

International audienceThe 6 April 2009 Mw 6.3 L'Aquila earthquake, central Italy, has been recorded by the Irpinia Seismic Network (ISNet) about 250 km southeast of the epicenter. Up to 19 three-component accelerometer stations could be used to infer the main source parameters with different seismological methods. We obtained an approximate location of the event from arrival times and array-based back-azimuth measurements and estimated the local magnitude (6.1) from an attenuation relation for southern Italy. Assuming an omega-square spectral model, we inverted S-wave displacement spectra for moment magnitude (6.3), corner frequency (0.33 Hz), stress drop (2.5 MPa), and apparent stress (1.6 MPa). Waveform modeling using a point source and an extended-source model provided consistent moment tensors with a centroid depth around 6 km and a prevalently normal fault plane solution with a dominant directivity toward the southeast. The relatively high corner frequency and an overestimated moment magnitude of 6.4 from moment tensor inversions are attributed to the rupture directivity effect. To image the rupture geometry, we implemented a beamforming technique that back-projects the recorded direct P-wave amplitudes into the earthquake source region. A northwest-southeast striking rupture of 17 km length is imaged, propagating with an average velocity up to 3 km/s. This value is significantly higher than our estimate of 2.2 km/s from S-wave spectra. Our case study demonstrates that the use of array techniques and a dense accelerometer network can provide quick and robust estimates of source parameters of moderate-sized earthquakes located outside the network

Automatic Picker Developments and Optimization: A Strategy for Improving the Performances of Automatic Phase Pickers

“…Distributions of time differences, in seconds, between automatic picks and corresponding manual picks within each class of manual picking-quality (see Table 1). Figure 7 shows examples of traces relative to a regional earthquake (2009/04/06 Aquila, Italy; Mw 6.3; Maercklin et al 2011) and to a local event (2009/05/18 Colliano, southern Italy; M L 2.5) with manual and automatic picks from PICK_ EW_OPT and FP_OPT. Each trace shows 10 s of signal, aligned with respect to the manual pick (located for all traces at 2 s).…”

Scisola: Real-Time Moment Tensor Monitoring for Seiscomp3

“…Other institutes -worldwide-that contribute to regional automatic MT calculation procedures are the Swiss Seismological Service (http://www.seismo.ethz.ch/prod/tensors/index_EN) and the Earthquake and Volcano Information Centre of Japan (http://wwweic.eri.u-tokyo.ac.jp/index-e.html), while (Bernardi et al, 2004) presented the first automatic MT inversion procedure in the Europe-Mediterranean region. MT retrieval software packages for regional distances include FMNEAREG (Delouis et al, 2008) and (Maercklin et al, 2011), KIWI (Cesca et al, 2010;Yagi and Nishimura, 2011) and ISOLA Zahradník, 2008, 2013). The last one has been used for research applications, for example, (Agurto et al, 2012;Quintero et al, 2014) (Triantafyllis et al, 2013) combined with the rapid evolution of the widely known seismological software, SeisComP3 (http://www.seiscomp3.org) (Weber et al, 2007), paved the way for the scisola (Triantafyllis et al, 2015) software implementation; a free and open-source code for automatic and real-time MT monitoring based on the ISOLA code and tightly connected to SeisComP3.…”

Ultra‐Low‐Noise Seismic Accelerometers for Earthquake Prediction and Monitoring

“…Earthquakes can be so small or distant (for example, in the ocean), that only lownoise or ultra-low-noise sensors are capable of measuring and monitoring small acceleration signals generated by such earthquakes [1][2][3][4][5]. In addition, such sensors can be used for the warning prediction system by detecting and monitoring of "preseismic" small changes on the ground that indicate that a significant quake is imminent [1,[5][6][7][8][9]. Ultra-low-noise seismic piezoelectric accelerometers with integral electronic (IEPE), also called integral electronic piezoelectric accelerometers or integrated circuit piezoelectric (ICP) accelerometers, are the best candidates for such purposes [10][11][12][13][14][15][16][17].…”

“…These networks record only seismic events; they cannot identify "preseismic" changes on the ground signaling that a significant quake is imminent. IEPE seismic accelerometers can be used in the seismic network similar to high-resolution seismic network (HRSN) capable of detecting microseismic fluctuations [3,[5][6][7][8][9]]. …”