Source of the 1693 Catania earthquake and tsunami (southern Italy): New evidence from tsunami modeling of a locked subduction fault plane,

The 1693 Catania earthquake, which caused 60000 deaths in eastern Sicily and generated a 5–10 m high tsunami, is investigated. GPS data indicate ESE‐WNW convergence in the Calabrian arc at 4–5 mm/yr. New high‐resolution seismic data image active compression at the toe of the accretionary wedge. The lack of instrumentally recorded thrust earthquakes suggests the presence of a locked subduction fault plane. Thermal modeling is applied to calculate the limits of the seismogenic zone. Tsunami modeling is performed to test the hypothesis that the 1693 earthquake occurred on the subduction fault plane (160 × 120 km in size) with 2 m of mean co‐seismic slip. This source successfully reproduces historical observations with regard to polarity and predicts 1–3 m high amplitudes. It is likely that only the SW segment of the subduction fault plane ruptured in 1693 and 1169, implying a recurrence interval of roughly 500 years for similar events

Reply to Comment on “The earthquakes of 29 July 2003, 12 February 2007, and 17 December 2009 in the region of Cape Saint Vincent (SW Iberia) and their relation with the 1755 Lisbon earthquake

Indeed, the Lisbon earthquake is a very unusual seismic event and an exception to the rule because most great tsunami-generating earth- quakes are related to well-defined subduction zones. The epicentral region, focal mechanism and the structures involved at the origin of this earthquake are still a matter of debate, with several models having been proposed (e.g. Baptista et al., 2003; Grandin et al., 2007a,b; Gutscher et al., 2006; Ribeiro et al., 2006; Vilanova et al., 2003; Zitellini et al., 2001)

Structural Controls on Crustal Fluid Circulation and Hot Spring Geochemistry Above a Flat‐Slab Subduction Zone, Peru

Hot spring geochemistry from the Cordillera Blanca and Cordillera Huayhuash, Peru, reveal the influence of crustal‐scale structures on geothermal fluid circulation in an amagmatic region located above a flat‐slab subduction zone. To test the influence of contrasting modes of faulting in these regions, springs were targeted along the Cordillera Blanca detachment fault, within its hanging wall, in the footwall of the detachment, and in the Cordillera Huayhuash. Hot springs along the Cordillera Blanca detachment fault zone are associated with recent extension and normal faulting, and those in its footwall and the Cordillera Huayhuash are located in the Marañon fold and thrust belt where compressional structures dominate. Springs along and in the hanging wall of the Cordillera Blanca detachment fault yield brackish‐saline, alkaline‐chloride waters, with oxygen, hydrogen, carbon, and chlorine stable isotope values that suggest mixing between meteoric groundwater and saline brine affected by high water‐rock interaction. Geothermometry reservoir temperature estimates (RTEs) of 91–226°C indicate maximum flow path depths of 8.7 or 11 km, depending on geothermal gradient, associated with the Cordillera Blanca detachment fault. In contrast, springs in the footwall and in the Cordillera Huayhuash exhibit a wide range of water types with an isotopic affinity to meteoric water, suggesting a greater influence from shallow groundwater and less water‐rock interaction. For these springs, RTEs of 40–98°C correspond to much shallower circulation (1.6–4 km). Results indicate that the Cordillera Blanca detachment system accommodates significantly deeper circulation of crustal fluids compared to other regional compressional structures

Les adakites et les andésites riches en Mg du volcan Pichincha (Equateur) : témoins de la fusion de la croûte océanique et de la métasomatose adakitique sous la zone volcanique nord des Andes

Situatedin the fore-arc of the Northern Volcanic Zone (NVZ) of the Andes in Ecuador, Pichincha volcano is an active edifice where have been erupted unusual magmas as adakites and high-Mg andesites. The particular geodynamic setting of the ecuadorian margin (i.e. the flat subduction of the Carnegie Ridge) suggests that thermo-barometric conditions for the partial melting of the oceanic crust are accomplished beneath this volcano. Pichincha adakites possess all the geochemical and isotopic characteristics of slab melts described in various other arc settings. High-Mg andesites with geochemical characteristics close to those of adakites present strong enrichments in MgO that suggest that, once they were produced by ca. 10 % partial melting of the downgoing subducted slab, some adakites en route to the surface strongly interacted with the peridotitic mantle wedge. Adakitic magmas could then represent, as in many other arcs where slab melting occurs, the principal metasomatic agent of the mantle in the NVZ in Ecuador

Ionian Abyssal Plain: a window into the Tethys oceanic lithosphere

The nature of the Ionian Sea crust has been the subject of scientific debate for more than 30 years, mainly because seismic imaging of the deep crust and upper mantle of the Ionian Abyssal Plain (IAP) has not been conclusive to date. The IAP is sandwiched between the Calabrian and Hellenic subduction zones in the central Mediterranean. A NNE–SSW-oriented 131&thinsp;km long seismic refraction and wide-angle reflection profile, consisting of eight ocean bottom seismometers and hydrophones, was acquired in 2014. The profile was designed to univocally confirm the proposed oceanic nature of the IAP crust as a remnant of the Tethys and to confute its interpretation as a strongly thinned part of the African continental crust. A P-wave velocity model developed from travel-time forward modelling is refined by gravimetric data and synthetic modelling of the seismic data. A roughly 6–7&thinsp;km thick crust with velocities ranging from 5.1 to 7.2&thinsp;km&thinsp;s−1, top to bottom, can be traced throughout the IAP. In the vicinity of the Medina seamounts at the southern IAP boundary, the crust thickens to about 9&thinsp;km and seismic velocities decrease to 6.8&thinsp;km&thinsp;s−1 at the crust–mantle boundary. The seismic velocity distribution and depth of the crust–mantle boundary in the IAP document its oceanic nature and support the interpretation of the IAP as a remnant of the Tethys lithosphere with the Malta Escarpment as a transform margin and a Tethys opening in the NNW–SSE direction.</p

Deep structure of the Ionian Sea and Sicily Dionysus - Cruise No. M111, October 10 - November 1, 2014, Catania (Italy) – Catania (Italy)

Summary The origin of the Ionian Sea lithosphere and the deep structure of its margins remain a little investigated part of the Mediterranean Sea. To shed light on the plate tectonic setting in this central part of southern Europe, R/V METEOR cruise M111 set out to acquire deep penetrating seismic data in the Ionian Sea. M111 formed the core of an amphibious investigation covering the Ionian Sea and island of Sicily. A total of 153 OBS/OBH deployments using French and German instruments were successfully carried out, in addition to 12 land stations installed on Sicily, which recorded the offshore air gun shots. The aim of this onshore-offshore study is to quantify the deep geometry and architecture of the Calabria subduction zone and Ionian Sea lithosphere and to shed light on the nature of the Ionian Sea crust (oceanic crust vs. thinned continental crust). Investigating the structure of the Ionian crust and lithospheric mantle will contribute to unravel the unknown ocean-continent transition and Tethys margin. Analyzing the tectonic activity and active deformation zones is essential for understanding the subduction processes that underlie the neotectonics of the Calabrian subduction zone and earthquake hazard of the Calabria/Sicily region, especially in the vicinity of local decoupling zones

Neotectonics of the SW Iberia margin, Gulf of Cadiz and Alboran Sea: a reassessment including recent structural, seismic and geodetic data

We use a thin-shell approximation for the lithosphere to model the neotectonics of the Gulf of Cadiz, SW Iberia margin and the westernmost Mediterranean, in the eastern segment of the Azores-Gibraltar plate boundary. In relation to previous neotectonic models in the region, we utilize a better constrained structural map offshore, and the recent GPS measurements over NW Africa and Iberia have been taken into account, together with the seismic strain rate and stress data, to evaluate alternative geodynamic settings proposed for the region. We show that by assuming a relatively simple, two-plate tectonic framework, where Nubia and Eurasia converge NW-SE to WNW-ESE at a rate of 4.5-6 mm yr-1, the models correctly predict the amount of shortening and wrenching between northern Algeria-Morocco and southern Spain and between NW Morocco and SW Iberia, as estimated from both GPS data and geological constraints. The consistency between modelled and observed velocities in the vicinity of Gibraltar and NW Morocco indicates that forcing by slab sinking beneath Gibraltar is not required to reproduce current horizontal deformation in these areas. In the Gulf of Cadiz and SW Iberia, the modelling results support a diffuse Nubia-Eurasia Plate boundary, where the convergence is accommodated along NNE-SSW to NE-SW and ENE-WSW thrust faults and WNW-ESE right-lateral strike-slip faults, over an area >200 km wide, in good general agreement with the distribution of the seismic strain rate and associated faulting mechanisms. The modelling results are robust to regional uncertainties in the structure of the lithosphere and have important implications for the earthquake and tsunami hazard of Portugal, SW Spain and Morocco. We predict maximum, long-term average fault slip rates between 1-2 mm yr-1, that is, less than 50 per cent the average plate relative movement, suggesting very long return periods for high-magnitude (Mw > 8) earthquakes on individual structures.publishe