Imaging evolution of Cascadia slow-slip event using high-rate GPS

The slip history of short-term slow slip event (SSE) is typically inferred from daily Global Positioning System (GPS) data, which, however, cannot image the sub-daily processes, leaving the underlying mechanisms of SSEs elusive. To address the temporal resolution issue, we attempted to employ the kinematic subdaily GPS analysis, which has never been applied to SSE studies because its signal-to-noise ratio has been believed too low. By carefully post-processing sub-daily positions to remove non-tectonic position fluctuation, our 30-minute kinematic data clearly exhibits the transient motion of a few mm during one Cascadia SSE. A spatiotemporal slip image by inverting the 30-minute data exhibits a multi-stage evolution; it consists of an isotropic growth of SSE followed by an along-strike migration and termination within the rheologically controlled down-dip width. This transition at the slip growth mode is similar to the rupture growth of regular earthquakes, implying the presence of common mechanical factors behind the two distinct slip phenomena. The comparison with a slip inversion of the daily GPS demonstrates the current performance and limitation of the subdaily data in the SSE detection and imaging.Better understanding of the non-tectonic noise in the kinematic GPS analysis will further improve the temporal resolution of SSE.

MIDDLE URAL EARTHQUAKE on October 18, 2015, ML=4.7, I0=6

Instrumental and macroseismic data on the earthquake of 18.10.2015 at 21h44m UTC, ML=4.7, I0=6 in the Sverdlovsk region, near the village of Sabik (Middle Urals) are presented. A significant amount of macroseismic data made it possible to build a map of the macroseismic field, taking into account the anisotropic nature of the propagation of the seismic effect. Taking into account the decision of the focal mechanism, the tectonic position of the source was substantiated.

Paleogeographic position of the central Dodecanese Islands, southeastern Greece: The push-pull of Pelagonia

The paleogeographic position of the central Dodecanese Islands at the transition between the Aegean and Anatolian plates plays a considerable role in understanding the link between both geologically unique domains. In this study, we investigate the tectonic history of the central Dodecanese Islands and the general correlation with the Aegean and western Anatolian and focus on the poorly studied islands of Kalymnos and Telendos. Three different major tectonic units were mapped on both islands from bottom to top: (1) The Kefala Unit consists of late Paleozoic, fossil-rich limestones, which have been deformed into a SE-vergent fold-and-thrust belt sealed by an up to 200-m-thick wildflysch-type olistostrome with marble and ultramafic blocks on a scale of tens of meters. (2) The Marina Basement Unit consists of a Variscan amphibolite facies basement with garnet mica schists, quartzites, and amphibolites. (3) Verrucano-type formation violet shales and Mesozoic unmetamorphosed limestones form the Marina Cover Unit. Correlation of these units with other units in the Aegean suggests that Kalymnos is paleogeographically located at the southern margin of the Pelagonian domain, and therefore it was in a structurally upper tectonic position during the Paleogene Alpine orogeny. New white mica 40Ar/39Ar ages confirm the Carboniferous deformation of the Marina Basement Unit followed by a weak Triassic thermal event. Single-grain white mica 40Ar/39Ar ages from pressure solution cleavage of the newly defined Telendos Thrust suggest that the Marina Basement Unit was thrusted toward the north on top of the Kefala Unit in the Paleocene. Located at a tectonically upper position, the units exposed in the central Dodecanese escaped subduction and the syn-orogenic, high-pressure metamorphism. However, these units were affected by post-orogenic extension, and the contact between the Marina Basement Unit and the non-metamorphic Marina Cover Unit has been reactivated by the cataclastic top-to-SSW, low-angle Kalymnos Detachment. Zircon (U-Th)/He ages from the Kefala and Marina Basement Units are ca. 30 Ma, which indicates that exhumation and cooling below the Kalymnos Detachment started in the Oligocene. Conjugate brittle high-angle normal fault systems, which resulted in the formation of four major WNW-ESE−trending graben systems on Kalymnos, localized mainly in the Marina Cover Unit and probably rooted in the mechanically linked Kalymnos Detachment. Since Oligo-Miocene deformation in the northern Dodecanese records top-to-NNE extension and the Kalymnos Detachment accommodated top-to-SSW extension, we suggest that back-arc extension in the whole Aegean realm and transition to the Anatolian plate is bivergent.

Isotopic evolution of prehistoric magma sources of Mt. Etna, Sicily: Insights from the Valle Del Bove

Mount Etna in NE Sicily occupies an unusual tectonic position in the convergence zone between the African and Eurasian plates, near the Quaternary subduction-related Aeolian arc and above the down-going Ionian oceanic slab. Magmatic evolution broadly involves a transition from an early tholeiitic phase (~ 500 ka) to the current alkaline phase. Most geochemical investigations have focussed on either historic (> 130-years old) or recent (< 130-years old) eruptions of Mt. Etna or on the ancient basal lavas (ca. 500 ka). In this study, we have analysed and modelled the petrogenesis of alkalic lavas from the southern wall of the Valle del Bove, which represent a time span of Mt. Etna’s prehistoric magmatic activity from ~ 85 to ~ 4 ka. They exhibit geochemical variations that distinguish them as six separate lithostratigraphic and volcanic units. Isotopic data (143Nd/144Nd = 0.51283–0.51291; 87Sr/86Sr = 0.70332–0.70363; 176Hf/177Hf = 0.28288–0.28298; 206Pb/204Pb = 19.76–20.03) indicate changes in the magma source during the ~ 80 kyr of activity that do not follow the previously observed temporal trend. The oldest analysed Valle del Bove unit (Salifizio-1) erupted basaltic trachyandesites with variations in 143Nd/144Nd and 87Sr/86Sr ratios indicating a magma source remarkably similar to that of recent Etna eruptions, while four of the five subsequent units have isotopic compositions resembling those of historic Etna magmas. All five magma batches are considered to be derived from melting of a mixture of spinel lherzolite and pyroxenite (± garnet). In contrast, the sixth unit, the main Piano Provenzana formation (~ 42–30 ka), includes the most evolved trachyandesitic lavas (58–62 wt% SiO2) and exhibits notably lower 176Hf/177Hf, 143Nd/144Nd, and 206Pb/204Pb ratios than the other prehistoric Valle del Bove units. This isotopic signature has not yet been observed in any other samples from Mt. Etna and we suggest that the parental melts of the trachyandesites were derived predominantly from ancient pyroxenite in the mantle source of Etna.

GEOCHEMISTRY AND PETROGENESIS OF OLIGOCENE DACITES FROM THE CENTRAL BOSNIA AND HERZEGOVINA WITH INSIGHT IN THE POST- COLLISIONAL TECTONIC EVOLUTION OF CENTRAL DINARIDIC OPHIOLITE BELT

Magmatic rocks of post-Late Eocene magmatic formation are widespread in the Sava segment of Sava- Vardar suture zone and adjoin areas. The rocks formed as a response to transpressional-transtensional tectonic activity preceded by the Cretaceous-Eocene compression of the Internal Dinarides and Tisia Unit as fragments of Eurasian continental lithosphere. Central Bosnia Tertiary volcanic rocks (CBTVR), erupted as dacites in Lower Oligocene, are peculiar rocks of this formation either by their location (southernmost distal outcrops) or geological setting (extrusive within the melange of the Internal Dinaride Ophiolite Belt). Major element composition of the CBTVR reveals high-K calc-alkaline geochemical affinity whereas trace element discriminate the rocks as shoshonitic. The rocks are LILE-enriched and show negative Ta- Nb, P and Ti anomalies, and positive Pb anomalies typical of subduction related volcanic rocks. Chondrite-normalized REE patterns exhibit significant LREE/HREE enrichment [(La/Yb)cn = 21.4 - 33.4]. Geochemical affinity of the CBTVR combined with tectonic position of extrusions suggests derivation of the melts from the subcontinental mantle which had inherited strong orogenic signature during an ancient subduction.

Late Glacial and postglacial seismicity in the Northeastern Fennoscandian Shield: tectonic position and age of paleo-earthquakes near Murmansk

Earthquake-induced deformations located near Murmansk City were investigated for information on the age, tectonic position and spatial occurrence of paleo-earthquakes. The main earthquake-generating zone is identified to be the system of strike slip faults and reverse-oblique faults trending NNW along the Kola River valley. We used radiocarbon analysis and paleogeographic reconstructions and revealed three episodes of increased seismic activity: from 9500 to 10500 cal BP, from 892 to 1182 cal BP, and from 200 to 300 cal BP. Based on the peak ground velocity estimation method we suggest that an earthquakes with a maximum moment magnitude up to Mw ≈ 6.0–6.5 may have taken place in the studied area. The recorded location of seismogenic deformation near faults indicates area of strong Late Glacial and Holocene earthquakes occurring in the northern Kola Peninsula; this is also consistent with observations concerning the historical events of 1772 and 1873, which took place near the area.Combined with previous data on palaeoseismicity in Kola region, our studies indicate a longer lasting and more complex spatial and temporal history of postglacial seismicity in the Northeastern Fennoscandian Shield area. In contrast to the generally accepted opinion, strong seismic events occurred not only during the deglaciation period or immediately after it, but continued until the late Holocene and the last centuries. Glacial isostasy as a factor giving rise to stresses has become minimal by the present time, while the tectonic factor continues to be felt.

First paleomagnetic and magnetic anisotropy results from Montenegro – the coastal area

&lt;p&gt;In the Southern part of Montenegro three main tectonic units are distinguished. The Dalmatian (South-Adriatic) zone is in the lowermost tectonic position and comprises shallow water Cretaceous carbonates, bauxites, Middle Eocene nummulitic limestones, transitional marls, and Upper Eocene flysch. It is thrusted over by the Budva zone characterized by deep water sediments of Triassic through Paleogene ages with tuffitic layers in the Ladinian. The uppermost unit is the High Karst zone developed in a carbonate platform environment from the Middle Triassic till the end of the Cretaceous. In this unit flysch sedimentation started after the K/T boundary.&lt;br&gt;From the above units we drilled and oriented in situ a total of 248 samples representing nine localities from the Dalmatian, six from the Budva and five from the High Karst zone, respectively. The harder rocks were drilled with portable gasoline powered, the softer ones with an electric drill. The laboratory measurements, demagnetizations, statistical evaluations of the measurements were carried out using standard methods in the Paleomagnetic Laboratory of the Mining and Geological Survey of Hungary.&amp;#160;&lt;br&gt;From the Dalmatian zone, the Upper Cretacous limestones have diamagnetic susceptibilities, very weak NRM, which either failed to provide statistically acceptable results (two localities) or obtained their remanence quite recently. The five flysch and transitional marl localities have well-defined AMS fabrics as well as paleomagnetic directions. The AMS fabrics must have been imprinted in a NE-SW oriented compressional strain field, which resulted in moderately strong fabrics with NW-SE oriented AMS lineations, perfectly following the Dinaridic trend recognized in Croatia. One locality, the only one with moderate tilt and rather poor statistical characteristics suggest post&amp;#8211;Eocene CCW, while those with steep dips have well-defined paleomagnetic directions, which are aligned with the intermediate AMS direction. The positive tilt test, however, provides an overall mean direction with absurdly shallow inclinations, which suggest that we are not dealing with &amp;#8220;real&amp;#8221; paleomagnetic directions, but maybe with magnetic anisotropy governed NRMs.&lt;br&gt;The rocks in the Budva zone show a large variation in lithological sense as well as in their magnetic properties. Except a Pietra Verde localitiy, the magnetic susceptibilities are weak, we can not define AMS fabrics, yet most of the localities yielded fairly good paleomagnetic results, which suggest pre-folding age of the acquisition followed by a large CW rotation of unit.&lt;br&gt;From the High Karst, only a single Lower Jurassic pelagic limestone provided paleomagnetic results which exhibit CW rotation. The others had weak magnetizations, diamagnetic susceptibilities and no or scattered magnetic signals.&lt;br&gt;This work was financially supported by the National Development and Innovation Office of Hungary project K 128625, by the Geological Survey of Montenegro and Ministry of Science and Education of Serbia project No. 176016.&lt;/p&gt;