Site effect studies following the 2016 Mw 6.0 Amatrice Earthquake (Italy): the Emersito Task Force activities

<em>On August 24, 2016, at 01:36 UTC a M_W6.0 earthquake struck an extensive area of the Central Apennines (Italy). It was followed by a large aftershock (M_W5.3, August 24, 02:33 UTC) and about 20 earthquakes with magnitude greater than 4.0, located between the towns of Norcia and Amatrice. Due to the mainshock magnitude and the widespread damaging level of buildings in the epicentral area, the Emersito task force has been mobilized by the Istituto Nazionale di Geofisica e Vulcanologia (INGV). The aim of Emersito is to carry out and coordinate the monitoring of local site effects, caused by geological and geomorphological settings. During the first days of the seismic emergency, Emersito installed a temporary seismic network for site effect studies at 4 municipalities close to the epicentral area (Amandola, Civitella del Tronto, Montereale and Capitignano), using 22 stations equipped with both velocimetric and accelerometric sensors. The selection of the sites where stations have been installed was mainly driven by the proximity to the epicentral area (without interfere with the rescue operation) and by peculiar geologic and geomorphologic settings (topographic irregularities, fault zones, alluvial plains).</em>

Determination of Source Parameters for Central and Eastern North American Earthquakes (1982–1986)

A search technique is applied to determine focal mechanisms from the surface-wave spectral amplitudes of recent earthquakes in the eastern U. S. and Canada. The technique provides the five source parameters of dip, slip, strike, depth, and seismic moment through a combination of criteria requiring best correlation coefficients, least residuals between theoretical and observed spectral-amplitudes and equality between independent seismic moment estimates from Love and Rayleigh wave data. This technique is applied to eight earthquakes of mb ≈ 5 that occurred in the North American continent in recent years. The focal mechanism results, constrained by P-wave first motions, indicate that near horizontal pressure axes are in the ENE-WSW for the 1982 Miramichi, New Brunswick (Canada) mainshock and one large aftershock (another large aftershock has ESE-WNW P-axis), the 1982 Gaza, New Hampshire mainshock, the 1982 Arkansas mainshock, the 1983 Goodnow, New York mainshock, and the 1986 Perry, Ohio mainshock. On the other hand a near horizontal tension axis in the direction NNE-SSW is found for the 1984 Wyoming mainshock in the western part of North American continent. The results obtained are consistent with the regional stress patterns and generally agree with the solutions of other investigators who used other aspects of the seismic wavefield.