Morphotectonic Observations Research Articles

The Petilia-Sosti Shear Zone (Calabrian Arc, southern Italy): An onshore-offshore regional active structure

The integrated interpretation of different types of data, consisting of a detailed Digital Terrain Model, field structural and morphotectonic observations, high resolution seismic data, seismological and Synthetic Aperture Radar interferometry information (vertical and horizontal movements), associated with a review of the available literature, has allowed to analyze the shallow expression of the regional-scale Petilia-Sosti Shear Zone (PSSZ). It is one of the major NW-trending tectonic lineaments affecting the Calabrian Arc and is characterized by a present-day tectonic and gravity-driven deformation. This study investigated the portion of the PSSZ between the offshore Crotone Peninsula, located along the Ionian sea of Calabria, and the central part of the Sila Massif.A complex tectonic history is documented since middle Miocene onward for the PSSZ. It consists of an alternation of sinistral and dextral transpressional and transtensional tectonic phases correlated with the geodynamic events occurred during the SE migration of the Calabrian Arc.The shallow expression of the investigated part of the PSSZ consists of a roughly 14 km wide, ca. 80 km long NW-trending tectonic zone including synthetic NW- to NNW-trending faults and N-NE antithetic minor structures. The main identified NW-trending faults, which show a development between 30 and 50 km, are the Sila and Lakes faults in the Sila Massif, and the Marcedusa-Steccato, Fosso Umbro and Tacina faults located in the SW part of the Crotone Basin and in its offshore area. Currently, the fault segments of the Sila Massif exhibit a prevailing normal kinematics with a left-lateral component, whereas a more complex geological framework occurs in the south-western part of the onshore-offshore Crotone Basin. The latter is dominated by gravity-driven movements, associated with the SE migration of the Crotone Megalandslide and with the regional uplift of Calabria, whereas normal kinematics with a small left-lateral component of movement, locally replaced by reverse/transpressional tectonics, was observed along the southern coast in the late Pleistocene deposits of the Le Castella marine terrace.The seismological data highlight that some strong earthquakes occurred in 1638, 1744 and 1832, with magnitude Mw between 5.7 and 6.8, might be associated with the Lakes, Fosso Umbro and Tacina faults respectively. In this frame, the PSSZ is proposed as a new potential NW-oriented active composite seismogenic source for the central-northern Calabria.

Denudation outpaced by crustal thickening in the eastern Tianshan

The modern high topography of the Tianshan resulted from the reactivation of a Paleozoic orogenic belt by the India/Asia collision. Today, the range exhibits tectonically active forelands and intermontane basins. Based on quantitative morphotectonic observations and age constraints derived from cosmogenic 10Be dating, single-grain post-infrared infrared stimulated luminescence (p-IR IRSL) dating and modeling of fault scarp degradation, we quantify the deformation in the Nalati and Bayanbulak intermontane basins in the central Eastern Tianshan. Our results indicate that at least 1.4 mm/yr of horizontal crustal shortening is accommodated within these two basins. This shortening represents over 15% of the 8.5 ± 0.5 mm/yr total shortening rate across the entire range at this longitude. This shortening rate implies that the Eastern Central Tianshan is thickening at a mean rate of ∼1.4 mm/yr, a rate that is significantly higher than the average denudation rate of 0.14 mm/yr derived from our cosmogenic analysis. This discrepancy suggests that the Tianshan range has not yet reached a steady-state topography and remains in a transient state of topographic growth, most likely due to limited denudation rates driven by the arid climate of Central Asia.

El Sistema de Falla Navarro: desplazamientos izquierdos a lo largo del Cinturón Deformado del Centro de Costa Rica

En este estudio se define el sistema de falla Navarro con base en observaciones geológicas, geomorfológicas y sismológicas. Este sistema de falla está localizado entre las estribaciones norte de la cordillera de Talamanca y las faldas sur y sureste de los volcanes Irazú y Turrialba y está caracterizado principalmente por desplazamientos de tipo sinestral. El sistema de falla Navarro tiene un rumbo entre este-oeste y noreste-suroeste e incluye los segmentos denominados: Tarrazú, Navarro, Cachí, Urasca, Paraíso y Maravilla. Dos estructuras transtensivas denominadas Estrella y Ujarrás están presentes a lo largo del sistema de falla. Sismos en el periodo 1973-2015 fueron relocalizados iluminando las fallas del sector suroeste del sistema. Los mecanismos focales calculados corresponden en su mayoría con fallas de desplazamiento de rumbo en concordancia con las observaciones morfotectónicas.

Active tectonics in the Malaga Basin: evidences from morphotectonic markers (Western Betic Cordillera, Spain)

The Malaga Basin is located in the westernmost part of the Betic Cordillera. This alpine cordillera in the south of Spain is the most active region of the Iberian Peninsula. Some of the most destructive earthquakes occurred historically in Spain took place within the Malaga Basin. In this work we focus on geomorphic and morphotectonic observations in the aim of finding active tectonic structures that could be seismogenic sources. First, we study the spatial arrangement and age of the Quaternary alluvial fan system as well as the drainage pattern of the basin, followed by the analysis of the distribution of regional markers like marine erosive surfaces and the extend of Pliocene marine deposits in the Malaga Basin. The tectonic structures inferred as active by the morphotectonic analysis are grouped into four main families: N60º-85ºE folds associated with blind thrust faults, N20º-30ºE and N40º-50ºE high angle dip-slip faults, and N165º-170ºE tear faults. Finally, their seismic potential in terms of maximum moment magnitude (Mw) is assessed by means of empirical relationships, varying between 6.0 and 7.0 depending on the hypothesis considered.

The 2010 Haiti earthquake: A complex fault pattern constrained by seismologic and tectonic observations

After the January 12, 2010, Haiti earthquake, we deployed a mainly offshore temporary network of seismologic stations around the damaged area. The distribution of the recorded aftershocks, together with morphotectonic observations and mainshock analysis, allow us to constrain a complex fault pattern in the area. Almost all of the aftershocks have a N‐S compressive mechanism, and not the expected left‐lateral strike‐slip mechanism. A first‐order slip model of the mainshock shows a N264°E north‐dipping plane, with a major left‐lateral component and a strong reverse component. As the aftershock distribution is sub‐parallel and close to the Enriquillo fault, we assume that although the cause of the catastrophe was not a rupture along the Enriquillo fault, this fault had an important role as a mechanical boundary. The azimuth of the focal planes of the aftershocks are parallel to the north‐dipping faults of the Transhaitian Belt, which suggests a triggering of failure on these discontinuities. In the western part, the aftershock distribution reflects the triggering of slip on similar faults, and/or, alternatively, of the south‐dipping faults, such the Trois‐Baies submarine fault. These observations are in agreement with a model of an oblique collision of an indenter of the oceanic crust of the Southern Peninsula and the sedimentary wedge of the Transhaitian Belt: the rupture occurred on a wrench fault at the rheologic boundary on top of the under‐thrusting rigid oceanic block, whereas the aftershocks were the result of the relaxation on the hanging wall along pre‐existing discontinuities in the frontal part of the Transhaitian Belt.

Active basins and neotectonics: morphotectonics of the Lake Ohrid Basin (FYROM and Albania)

The Lake Ohrid Basin in FYROM (Former Yugoslav Republic of Macedonia) and Albania meets all criteria of an active, seismic landscape: linear step-like fault scarps in the landscape and under water within the lake. Post-glacial (or Late Pleistocene) bedrock fault scarps at Lake Ohrid are long-lived expressions of repeated surface faulting in tectonically active regions, where erosion cannot outpace the fault slip. Other morphotectonic features are wind gaps, wineglass-shaped valleys and triangular facets, which are well preserved. Generally, the faults and fault scarps are getting younger towards the basin centre, as depicted on seismic and hydroacoustic profiles. Additionally, mass movement bodies within the lake and also onshore (rockfalls, landslides, sub-aquatic slides, homogenites, turbidites) are likely to have been seismically triggered. These morphotectonic observations are in line with focal mechanisms of earthquakes in the greater Lake Ohrid area. We investigated the neotectonic history and tectonic geomorphology of the Lake Ohrid Basin by means of an integrated multidisciplinary approach, using tectonic geomorphology and a variety of geophysical and remote sensing methods.

A re-evaluation of the Eskişehir Fault Zone as a recent extensional structure in NW Turkey

The Eskişehir Fault Zone (EFZ), one of the major active structures within the Anatolian platelet, is investigated in a 100 km long sector between Bozüyük and Alpu, in vicinity of Eskişehir. The morphotectonic observations indicate that throughout the studied area the EFZ extends WNWwards as a ca. 15 km wide belt, and is composed of some 21 fault segments, 5–25 km long. These segments form a north-dipping southern set and two south-dipping northern sets, all together working both sides of the Eskişehir graben. The faults are dominantly normal in character with a slight right-lateral component in the westernmost areas. The estimated total vertical displacement on certain northern and southern fault segments exceeds 450 m. In order to estimate the initiation age of the EFZ a brief stratigraphic review is given. The generally horizontal Pliocene terrestrial deposits are separated from the Miocene succession by a low-angular unconformity, and are cut in turn by the EFZ. Sedimentological data show that neither the distribution of the Pliocene depositional environments and their paleocurrent directions, nor the preserved Pliocene basal unconformity surface have a genetic relation to the EFZ. These data strongly suggest that the EFZ is a younger post-Pliocene active normal fault zone with low rates of deformation.

Recognition of past earthquakes along the Sparta fault (Peloponnesus, southern Greece) during the Holocene, by combining results of different dating techniques

Abstract Sparta fault is an impressive landform, located on the eastern front of Taygetos mountain, southern Greece. Detailed morphotectonic observations on this fault suggest that it should be active at least since Early Quaternary. However, according to the current seismological knowledge, this region is characterized by very low seismicity. The only reported earthquake to have occurred in this area is that of 464 b . c ., a destructive event that devastated the whole city of Sparta. In order to get information on the occurrence of past earthquakes during the Holocene, results of different independent dating works that have performed along the Sparta fault were used. These researchers confirm the existence not only of the 464 b . c . earthquake but also of several more that occurred at ca. 3900 b . c ., 2500 b . c . and 2000 b . c ., 550 a . d . and 1000 a . d . The events that occurred at 2500 and 464 b . c . should correspond to major events of magnitude of the order of 7, which ruptured the entire length of the fault, while these at 3900 b . c ., 2000 b . c ., 550 a . d . and 1000 a . d ., to smaller events of magnitude 6–6.5. The return periods of strong earthquakes along the Sparta fault is estimated to be around 2000 years, but within these periods events of smaller magnitude that ruptured segments of the fault have also occurred.

Seismic Hazard Assessment in the Area of Mystras-Sparta, South Peloponnesus, Greece, Based on Local Seismotectonic, Seismic, Geologic Information and on Different Models of Rupture Propagation

Strong seismic events once again confirm the view that great destructive earthquakes are produced by the reactivation of pre-existing faults although they have usually remained inactive for many, perhaps thousands of years. It is evident that such active seismogenic zones, with little or no seismicity, have presumably been ignored in the determination of the region's seismic hazard. At south Peloponnesus, Greece, is situated at Taygetos mountain. At its eastern front lies a large normal fault system, the southern segment being the Sparta fault. This area has been characterized by low seismicity for the last 25 centuries. However, during the 6th and 5th centuries B.C. several destructive earthquakes have been reported. That of 464 B.C., was the most destructive and devastated the city of Sparta. Detailed morphotectonic observations of this area, suggest that the earthquake of 464 B.C. could be related to the most recent reactivation of this fault. The ground accelerations that would be produced by a future activation of the Sparta fault, were calculated, by applying a method which takes into account information mainly from the seismotectonic parameters of the Sparta fault, the rupture pattern, the properties of the propagation medium and the local ground conditions. Moreover, these results were compared with those of other independent studies based mainly on the seismic data of the area. This method estimated greater expected values of ground acceleration than those computed by the conventional seismic hazard methods. The highest values correspond to the activation of the Sparta fault either in a unilateral rupture, which would start from the southernmost point of the fault, or in a circular one. Furthermore, an increase is observed of the order of 50% in the ground acceleration values in unconsolidated soft ground in relation to the corresponding values of hard ground.

Geomorphic and morphotectonic observations in the drainage network of Kakotopia Stream, North East Attica, Greece

The Kakotopia stream, located in north-east Attica, flows north into the South Euboic gulf. The drainage basin of Kakotopia is composed of schists, marbles and fluviotorrential deposits. The contact between the marbles and schist system in most cases is tectonic defined by several fault surfaces; in other instances, the contact is transitional. There are numerous neotectonic faults in the region, having a prevailing SE-NW direction, which form small tectonic horsts and grabens, usually filled with recent deposits. An asymmetric anticlinal structure is also observed plunging towards the SW. A large part of the lower reaches of the drainage system of Kakotopia stream is most probably missing. This is owed to the presence of major faults having an ESE-WNW direction parallel to today's coastline. The creation of the South Euboic gulf depression during the Quaternary is attributed to the presence of these faults. The upper section of the drainage system is controlled to a great extent by the tectonic activity of the area. In this part, we observe the phenomenon of stream piracy which is owed not only to fault tectonism but also to the differential erosion rates of the marbles and the schists.

Active thrust tectonics in western Sicily (southern Italy): the 1968 Belice earthquake sequence

ABSTRACTThe 1968 Belice earthquake sequence, characterized by six main shocks with 5 < M < 5.4, represents the strongest seismic event recorded in western Sicily in historical times. The epicentral area is located in the Belice Valley, a region lacking any topographic lineament likely to result from a fault with significant offsets of any kind. Instrumental data show that hypocentres of the major shocks are distributed along a roughly N‐dipping plane extending from about 36 km to 1 km depth. Fault plane solutions show pure thrusting mechanisms on N‐dipping, ENE‐trending planes, or oblique slip with a right‐lateral component of motion along steep WSW‐dipping planes, both as a result of approximate N‐S shortening. The observed destruction indicates that isoseismal areas are elongated in an ENE direction. Similarly, the epiccntral distribution of events with M ≥ 4 outlines a roughly elliptical ENE‐elongated area located 20 km NW of the Sciacca‐Rocca Ficuzza thrust front. This ENE‐striking structure, representing the regional morphotectonic feature closest to the epicentral area, consists of two main imbricate fan systems. In the southernmost system, Quaternary deposits (tentatively dated as 1.0–0.7 Myr old) are involved in a large ramp anticline uplifting them to a maximum altitude of 346 m. The occurrence of Holocene lacustrine piggy‐back basins on the rear of this structure also indicates late Quaternary activity of the underlying thrust. Seismological, structural and morphotectonic observations suggest that multiple ruptures might have occurred during the 1968 sequence on a blind crustal thrust ramp located beneath the epicentral area. Slip propagated southwards along the shallow ramp‐flat system characterizing the thin‐skinned foreland fold and thrust belt of southwestern Sicily, being dispersed in flexural folding processes and diffuse strain along this path.

Surface faulting caused by the Kalamata (Greece) earthquakes (13.9.86)

A great number of neotectonic faults traverse the Messinian gulf and its geological prolongation on the continent towards the north, which forms the Kalamata-Kyparissia tectonic graben. On the 13th September 1986, the whole Messinia area was shaken by an earthquake ( M = 6.2); it caused much damage, mainly in the city of Kalamata. Catastrophes were limited to a relatively small area, in the form of a triangle. The striken area is a second-order tectonic graben (called the Dimiova-Perivolakia graben) which is developed on the eastern margin of the greater Kalamata-Kyparissia tectonic graben. Alpine and post-Alpine (Neogene and Quaternary) formations outcrop in the graben. The recent earthquakes caused small fractures (4–5 m long) and small-scale reactivation of neotectonic faults. Both have been observed in almost all formations. The seismic fractures form a zone or zones. They consist of small parallel fractures arranged en échelon, which allows us to conclude that in some places the fracture zones are of right-lateral and in others of left-lateral character. This, in fact, coincides with the kinematics of the main neotectonic fault-zones of the graben. This, in conjunction with other morphotectonic observations, suggests that the deformation of the area is connected with coupling or even torsion phenomena.

In situ structural observations along Transform Fault A in the FAMOUS area, Mid-Atlantic Ridge

Two areas of Transform Fault A were explored in situ during the FAMOUS project. Ten dives were conducted with the diving saucer Cyana in the median part and five dives with the bathyscaph Archimede near the western intersection with the rift valley. The resulting field observations are the first made along an oceanic transform fault with a resolution similar to the one obtained with morphotectonic observations on land. The existence of left-lateral motion predicted by the plate-tectonics model is demonstrated with the help of micro-tectonic observations on fault scarps. However, the surface expression of the transform fault does not consist of a unique or major fault. Instead, the fault pattern is complex and variable, in the north-south as well as the east-west directions, although the width of the active zone of transform faulting is small (300 to 1,000 m). A comparison of the north-south sections of the transform fault made in the two areas leads to the conclusion that its dynamics have evolved in a complex way through time. The significance of the axial deep and its associated rubble cover is discussed in this context.