Publication Date:
2017-04-04
Description:
Seismicity in Eastern Sicily as recorded by the Submarine Network-1 seafloor observatory (SN-
1) in the period from 2002 October to 2003 May is examined with the aim of identifying the as
yet poorly known seismogenic zones placed in the Ionian basin, where some of the strongest
earthquakes have occurred. A comparison between the seismic recordings of land networks
and the seafloor station has allowed us to focus on low-magnitude seismicity only recorded by
SN-1.We have analysed 239 high-quality events from among a total of 485 seismic signals not
included in the land-based network bulletins. The waveform features and the possible source
zones for those events are investigated by means of polarization and particle motion techniques.
Most of the 239 events (213) are characterized by high values of rectilinearity typical of P- and
S-arrival particle motions, while the remaining 26 events have different polarization features,
with an emergent first phase and prevalently planar polarization.We have interpreted the latter
signals as being associated to submarine landslides. From particle motion analysis, we have
determined the azimuthal distribution of the events and the incidence angles of P waves in
respect to the Observatory with the aim of determining their distribution in relation to the active
but scarcely known structural setting of the off-shore area. Moreover, the integrated locations
of some earthquakes occurring in the study area and recorded by SN-1 and land stations was
performed to determine the apparent P-wave velocity necessary to calculate source-station
distances. As an additional result of the integration, we have obtained more accurate locations
of earthquakes occurring in the coastal and off-shore areas of Eastern Sicily, associated with
reduced horizontal and vertical errors and significantly lower values of azimuthal gaps. Lastly,
a location distribution of the 213 analysed events was obtained by setting two conditions:
(1) a maximum epicentral distance to a fixed depth coinciding with the depth of the seafloor
station and (2) a minimum epicentral distance associated to the maximum depth of events.
Accordingly, two patterns of seismicity were determined for the maximum and the minimum
expected spread of the hypocentres. The main features of both patterns are a diffuse seismicity
in the Western Ionian basin with a major epicentre density SE of SN-1 and a depth of most
of the events within 60 km. Local magnitude determination was also performed, taking into
account an attenuation law proposed for Southeastern Sicily. Despite the uncertainties in the
location distribution using single-station recordings, the results show diffuse seismicity all
around SN-1 and, in particular, in the off-shore area.
Description:
Published
Description:
490-501
Description:
1.4. TTC - Sorveglianza sismologica delle aree vulcaniche attive
Description:
JCR Journal
Description:
reserved
Keywords:
Earthquake locations
;
Ionian Sea (off-shore Eastern Sicity)
;
local seismicity
;
seafloor observatory
;
wave polarisation
;
04. Solid Earth::04.06. Seismology::04.06.06. Surveys, measurements, and monitoring
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
article
Format:
580522 bytes
Format:
application/pdf
