fast geodetic strain-rates in eastern sicily: new insights ... › gngts › files › 2014 › s11...

Fast geodetic strain-rates in eastern Sicily: New insights into block tectonics and

seismic potential in the area of the great 1693 earthquake

Serpelloni E.,1 Mastrolembo B.,1 Argnani A.,2 Bonforte A.,1 Burgmann R.,3

Anzidei M.,1 Baldi P.,4 Puglisi G.1

Sessione 1.1 Sismicità e Faglie: Ieri, Oggi, Domani

1) INGV, 2) ISMAR-CNR, 3) UC Berkeley, 4) UNIBO

Goals, Data and Methods

•We studied the kinematics of Eastern Sicily, locus of some of the largest historical earthquakes of the Mediterranean

•Here GPS measurements already showed high strain rates and sudden changes in the speed and direction of surface motions (e.g., Serpelloni et al., 2010; Palano et al., 2012)

•We used a new GPS velocity field and elastic dislocation models to provide new constraints on the kinematics of Sicily in the framework of the broader Nubia-Eurasia plate convergence

•We highlight a fragmentation of the Sicily µ-plate into 3 smaller tectonic blocks, which move independently from Nubia, describing an overall clockwise rotation of this crustal domain with respect to Eurasia.

01/12

We focus on southeastern Sicily, where the causative fault of the great 1693 earthquake is still matter of debate. Here, a dense geodetic network can provide useful information about active faults that are likely accommodating the observed high deformation rates.

Visini et al., 2009

Goals, Data and Methods 01/12

Tectonic and Kinematic Settings

Velocities of cGPS sites w.r.t. Eurasia Velocities of cGPS sites w.r.t. Nubia

02/12

Velocities of cGPS sites w.r.t. Eurasia Velocities of cGPS sites w.r.t. Nubia

1

2

3

Tectonic and Kinematic Settings 02/12

160x10-9/yr 120x10-9/yr

Velocities of cGPS (red) and eGPS (blue) sites w.r.t. Eurasia. Survey data on the Hyblean network collected between 1994 and 2006


Bonforte et al., 2002

Mattia et al., 2012

Palano et al., 2012

Velocities of cGPS (red) and eGPS (blue) sites w.r.t. Eurasia. Survey data on the Hyblean network collected between 1994 and 2006

160x10-9/yr 120x10-9/yr


Kinematic Block Model

• We developed a kinematic block model that accounts for rotation of crustal blocks and elastic strain accumulation at blocks-bounding faults.

• We accounted for two different kinematic boundary conditions of the Nubia (Ionian) - Calabria relative motion (see D’Agostino et al., 2008; Serpelloni et al., 2010).

• We tested different blocks configurations, of increasing complexities, describing a tectonic fragmentation of the study area

Ionian block moving accordingly to the Nubian plate Ionian block moving accordingly to the Apulian µ-plate

04/12

A systematic chi-square reduction and F-tests confirm the hypothesis that the Sicily block moves independently from the Nubian plate, highlighting a internal fragmentation of the Sicily domain into three smaller tectonic blocks:

1) a central Sicily block (SICI)

The relative motion of the three tectonic blocks explains the measured geodetic deformation in Sicily

1

Kinematic Block Model 05/12

1

2



1) a central Sicily block (SICI)2) a southeastern Sicily (Hyblean) block (SESI)


Malta escarpmentScicli-RagusaLentini Graben?

1

2

3



1) a central Sicily block (SICI) 2) a southeastern Sicily (Hyblean) block (SESI) 3) a northeastern Sicily block (NESI)


S. Tyrrhenian

Etna-CefalùTindari-Gardini

Blocks, Slip Rates & Tectonics

The final block model well reproduces the observed GPS velocities, and the resulting block-bounding faults kinematics is in agreement with seismotectonics* and geological information

06/12

Blocks, Slip Rates & Tectonics

April, 13 2012 MW 4.4

The final block model well reproduces the observed GPS velocities, and the resulting block-bounding faults kinematics is in agreement with seismotectonics* and geological information

* this is particularly evident for the NESI block, where focal mechanisms highlight changes in the tectonic regimes along the block boundary (Pondrelli et al., 2004; Argnani et al., 2007; Billi et al., 2010)

06/12

Shortening & Extension in Eastern Sicily

We tested different geometries and positions of the northern Hyblean block fault bound, starting from seismogenic faults suggested in the literature (e.g., DISS, ITHACA).

07/12

For the Etna-Palermo lineament, we find a reasonable fit using a vertical dislocation, locked at 10-20 km depth (4 mm/yr slip rate)

Shortening & Extension in Eastern Sicily 08/12

We performed a systematic search moving the position, dip and locking depth of the northern boundary of the Hyblean block

LDEC=10 km

LDEC=20 km

LDEC=30 km

The velocity gradients are best explained by a reverse slip (at 5 mm/yr) on a N-dipping (S-verging) high-angle (60-80°) fault located in the Catania plain, with a locking depth of ~5 km + extension(at 4 mm/yr) on the ESE-WNW trending Etna-Cefalù-Palermo line, approximated by a vertical, 10 km locked, planar fault.

09/12Shortening & Extension in Eastern Sicily

Tectonic Inversion of Flexural Faults

Modified from Longaretti et al., 1991

10/12

The position of this fault segment and its steep northward dip angle well correlate with the presence of high-angle faults beneath the Catania plain, being part of the system of flexural faults that affected the Hyblean foreland (Longaretti et al., 1991).

These extensional faults formed during the early Pliocene flexure of the Hyblean foreland under the load of the Maghrebian fold-and-thrust belt.

Implications for Seismic Hazard 11/12

Limited locking depth and length of the reverse faults system in the Catania plain suggest that this is unlikely the source of a M>7 earthquake. The relatively high slip-rate and the limited instrumental seismicity recorded in the area require additional investigations in order to better characterize its seismic potential and possible partitioning of shortening across multiple closely spaced faults (common in inversion tectonic environments)

The Etna–Palermo lineament shows coherent seismotectonic and geodetic features. The relatively high slip-rate (∼4 mm/yr) is likely partitioned on several, smaller, fault segments, being part of a geologically recent reactivation of preexisting crustal discontinuities

Geodetic slip-rates of ∼1 mm/yr are modeled for the Scicli-Ragusa fault, however, further investigations are required to better characterize the seismic potential of this fault system, since our results rely on modeling rather than on direct measurements of geodetic

Conclusions

• GPS velocities and elastic block models reveal a tectonic fragmentation of Sicily

• The Sicily domain rotates clockwise w.r.t. Eurasia and it is fragmented into three smaller tectonic blocks whose relative motions explain the measured geodetic deformation and tectonic regimes at blocks boundaries

• From N to S, eastern Sicily shows rapid changes in the style of geodetic deformation. This pattern is explained by the relative motion of the three tectonic blocks, accommodated across re-activated crustal discontinuities, characterized by poor surface geological expressions

• We defined the kinematic role of two fault systems, the Etna–Palermo lineament and high-angle reverse faults in the Catania plain, that are not accounted in active fault databases (e.g., DISS, SHARE) and for which additional investigations are required to confirm or re-define their seismogenic potential

• Our results support the view that the present-day kinematics of the Mediterranean is only subordinately driven by the Nubia-Eurasia convergence. The dynamics of the Mediterranean subduction system is likely playing an active role in governing block motions and active tectonics

12/12

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fast geodetic strain-rates in eastern sicily: new insights ... › gngts › files › 2014 › s11...

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