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Evidence for surface rupture associated with the Mw 6.3 L'Aquila earthquake sequence of April 2009 (central Italy)

EMERGEO Working Group

An earthquake of Mw = 6.3 struck L'Aquila town (central Italy)
on 6 April 2009 rupturing an ca.18-km-long SW-dipping normal
fault. The aftershock area extended for a length of more than
35 km and included major aftershocks on 7 and 9 April and
thousands of minor events. Surface faulting occurred along the
SW-dipping Paganica fault with a continuous extent of
ca.2.5 km. Ruptures consist of open cracks and vertical dislocations
or warps (0.1m maximum throw) with an orientation of
N130°–140°. Small triggered slip and shaking effects also took
place along nearby synthetic and antithetic normal faults. The
observed limited extent and small surface displacement of the
Paganica ruptures with respect to the height of the fault scarps
and vertical throws of palaeo-earthquakes along faults in the
area put the faulting associated with the L'Aquila earthquake in
perspective with respect to the maximum expected magnitude
and the regional seismic hazard.

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Clues to the identification of a seismogenic source from environmental effects. The case of the 1905 Calabria (southern Italy) earthquake.

A. Tertulliani and L. Cucci

ABSTRACT

The September 8, 1905 Calabria (southern Italy) earthquake belongs to a peculiar family of highly destructive (I0=XI) seismic events, occurred at the dawning of the instrumental seismology, for which the location, geometry and size of the causative source are still substantially unconstrained. During the century elapsed since the earthquake, previous Authors identified three different epicenters that are more than 50 km apart and proposed magnitudes ranging from M≤6.2 to M=7.9. Even larger uncertainties were found when the geometry of the earthquake source was estimated. In this study, we constrain the magnitude, location and kinematics of the 1905 earthquake through the analysis of the remarkable environmental effects produced by the event (117 reviewed observations at 73 different localities throughout Calabria). The data used in our analysis include ground effects (landslides, rock falls and lateral spreads) and hydrological changes (streamflow variations, liquefaction, rise of water temperature and turbidity). To better define the magnitude of the event we use a number of empirical relations between seismic source parameters and distribution of ground effects and hydrological changes. In order to provide constraints to the location of the event and to the geometry of the source, we reproduce the coseismic static strain associated with different possible 1905 causative faults and compare its pattern to the documented streamflow changes. From the analysis of the seismically-induced environmental changes we find that: 1) the 1905 earthquake had a minimum magnitude M=6.7; 2) the event occurred in an offshore area west of the epicenters proposed by the historical seismic Catalogs; 3) it most likely occurred along a 100°N oriented normal fault with a left-lateral component, consistently with the seismotectonic setting of the area.

http://www.nat-hazards-earth-syst-sci.net/9/1787/2009/nhess-9-1787-2009.html

L’AQUILA (CENTRAL ITALY) EARTHQUAKES: THE PREDECESSORS OF THE APRIL 6, 2009 EVENT

Andrea Tertulliani, Antonio Rossi, Luigi Cucci, Maurizio Vecchi

On April 6th 2009 a Mw=6.3, Imax=9-10 earthquake struck the Abruzzi region of Central Italy (http://portale.ingv.it/highlights/view?set_language=en). We find similarities in some peculiar characteristics of the 2009 sequence and of some historical events occurred in the area, in particular in 1461 and 1762. We observe strong analogies in the distribution of the intensities and in the areas of the strongest effects produced by these shocks, as well as in the temporal evolution.

The 2009 quake severely devastated the town of L’Aquila (~73,000 inhabitants) and tens of villages located along the Middle Aterno Valley (hereinafter MAV, see Figure 1). One month after the event, its social impact was not yet definitive but certainly burdensome: 308 casualties, 47% homes damaged in the epicentral area, 20% heavily damaged (with an even worse situation in downtown L’Aquila), and about 40,000 people left homeless.

Although the magnitude of the event was not among the largest to have occurred in the Apennines, the Abruzzi earthquake can be considered as one of the most disastrous of the last century. The effects of the shaking were recorded not only in the epicentral zone but also in distant areas (e.g. as far as Rome - ~90 km from the epicenter – where it produced light damage), and heavily affected the cultural and socio-economic fabric of a wide region characterized by high seismic risk.