Does Deep Tectonic Tremor Occur in the Central‐Eastern Mediterranean Basin?

Tectonic tremor has been observed at the roots of many fault systems around the Pacific rim, including convergent and transform plate boundaries. The extent to which deep tremor signals are prevalent along fault systems elsewhere, including the Mediterranean basin, has not yet been documented in detail. A body of evidence suggests that tremor triggered during the surface waves of teleseismic events may commonly occur where ambient tremor during episodic tremor and slip episodes occur, suggesting triggered tremor provides a useful tool to identify regions with ambient tremor. We perform a systematic search of triggered tremor associated with large teleseismic events between 2010 and 2020 at four major fault systems within the central-eastern Mediterranean basin, namely the Hellenic and Calabrian subduction zones, and the North Anatolian and Kefalonia transform faults. In addition, we search for ambient tremor during a slow slip event in the eastern Sea of Marmara along a secondary branch of the North Anatolian Fault, and two slow slip events beneath western Peloponnese (Hellenic Subduction Zone). We find no unambiguous evidence for deep triggered tremor, nor ambient tremor. The absence of triggered tremor at the Hellenic and Calabrian subduction zones supports an interpretation of less favorable conditions for tremorgenesis in the presence of old and cold slabs. The absence of tremor along the transform faults may be due to an absence of the conditions commonly promoting tremorgenesis in such settings, including high-fluid pressures and low-differential stresses between the down-dip limit of the seismogenic layer and the continental Moho

Possible relationship between Seismic Electric Signals (SES) lead time and earthquake stress drop

Stress drop values for fourteen large earthquakes with MW ≥ 5.4 which occurred in Greece during the period 1983–2007 are available. All these earthquakes were preceded by Seismic Electric Signals (SES). An attempt has been made to investigate possible correlation between their stress drop values and the corresponding SES lead times. For the stress drop, we considered the Brune stress drop, ΔσB, estimated from far field body wave displacement source spectra and ΔσSB derived from the strong motion acceleration response spectra. The results show a relation may exist between Brune stress drop, ΔσB, and lead time which implies that earthquakes with higher stress drop values are preceded by SES with shorter lead time

LS-ADT: Lightweight and scalable anomaly detection for cloud datacentres

© Springer International Publishing Switzerland 2016. Cloud data centres are implemented as large-scale clusters with demanding requirements for service performance, availability and cost of operation. As a result of scale and complexity, data centres typically exhibit large numbers of system anomalies resulting from operator error, resource over/under provisioning, hardware or software failures and security issus anomalies are inherently difficult to identify and resolve promptly via human inspection. Therefore, it is vital in a cloud system to have automatic system monitoring that detects potential anomalies and identifies their source. In this paper we present a lightweight anomaly detection tool for Cloud data centres which combines extended log analysis and rigorous correlation of system metrics, implemented by an efficient correlation algorithm which does not require training or complex infrastructure set up. The LADT algorithm is based on the premise that there is a strong correlation between node level and VM level metrics in a cloud system. This correlation will drop significantly in the event of any performance anomaly at the node-level and a continuous drop in the correlation can indicate the presence of a true anomaly in the node. The log analysis of LADT assists in determining whether the correlation drop could be caused by naturally occurring cloud management activity such as VM migration, creation, suspension, termination or resizing. In this way, any potential anomaly alerts are reasoned about to prevent false positives that could be caused by the cloud operator’s activity. We demonstrate LADT with log analysis in a Cloud environment to show how the log analysis is combined with the correlation of systems metrics to achieve accurate anomaly detection

Neotectonic study of the Western Crete. Seismic risk evaluation of the active faults

A detailed study has been realized in the framework of a large-scale seismotectonic survey in Western Crete (Southern Greece), for the creation of a revised neotectonic map in a scale of 1:50.000, including the recognition and mapping of the main neotectonic faults and the evaluation of their seismic potential. For this reason, the faults under investigation were distinguished as active, possible active and inactive. Kinematic data and striations were used to estimate the corresponding stress field geometry. Two distinctive stress phases were recognized, operating after the Middle Miocene extensional exhumation of deep crustal rocks. The first N-S extension phase (D1) took place during Mid-Upper Miocene to Lower Pliocene, forming large normal faults, trending mainly E-W, that bound the large Neogene basins. The second phase (D2) took place during late Pliocene-Quaternary times, forming medium-to-large normal faults that trend mainly N-S, related to an E-W extension. In the E-W trending D1 faults, a younger strike-slip striation usually occurs, compatible with the later D2 kinematics. Smaller, mainly NE-SW trending faults, with significant lateral displacement, indicate a kinematic compatibility to the more recent D2 phase. Some of these faults act as transfer zones between the larger N-S trending D2 faults. Considering the fault length and the using several geological criteria for their seismic risk evaluation, we recognized 13 large major fault zones in the study area, six of which were considered as active, while three as possible active faults. Results obtained from the analysis of fault plane solution information verify both the determined active (D2 phase) stress field results, as well as the local kinematic behavior of the neotectonic faulting. Moreover, a detailed seismic hazard analysis, involving both probabilistic and deterministic approaches, shows a significant spatial variation of the various hazard measures, with the seismic hazard of the westernmost part of study area being controlled by the neighboring higher seismicity neotectonic fault

Neotectonic analysis, active stress field and active faults seismic hazard assessment in western crete

Within the framework of this study the complicated fault system of Western Crete was napped in detail and its kinematic and dynamic setting was analysed in order to distinguish 13 major active and possible active fault zones, the seismic potential of which was assessed. Moreover, kinematic data and striations were used to estimate the corresponding stress field geometry. Two stress phases were recognized: 1st the N-S extension phase (D1) in Mid-Upper Miocene to Lower Pliocene times forming E-W normal faults that bound the Neogene basins; 2nd the E-W extension phase (D2) in Late Pliocene-recent times forming N-S trending active normal faults. Smaller, mainly NE-SW trending faults, with significant strike-slip component, indicate a kinematic compatibility to the D2 phase, acting as transfer faults between larger N-S fault zones. The faults were incorporated in a detailed seismic hazard analysis together with the available seismological data, involving both probabilistic and deterministic approaches, for seismic hazard assessment of several selected sites (municipalities)