Faulting associated with historical and recent earthquakes in the Eastern Mediterranean region

This paper summarizes evidence for surface faulting in historical and recent earthquakes in the Eastern Mediterranean region and in the Middle East. Such information is particularly important for studies of active tectonics and for palaeoseismology. We have found 78 cases of faulting pre-1900 and 72 post-1900, some of which show that faults that have apparently been inactive this century had already ruptured before 1900. For some cases faulting could not have been predicted from 20th century activity, and in others it could have been expected, but has not been observed during the instrumental period. The data are sufficient to allow the derivation of relationships between magnitude and rupture length.     

The Rhodes earthquake of 26 June 1926

We use macroseismic and instrumental data to re-examine the large earthquake of 26 June 1926 in the Hellenic Arc and other associated events. The earthquake was felt over a large area in the Eastern Mediterranean region and caused sporadic damage, and in places destruction, over a large area in Rhodes, southwestern Anatolia, eastern Crete and in the Nile Delta. Despite its size, there has been uncertainty as to its position, depth and magnitude. The earthquake was well recorded instrumentally and we have relocated it using the readings listed in the International Seismological Summary and the present location procedure of the International Seismological Centre. We have also inspected seismograms from 14 stations. We find the intermediate depth of the event to be well established at about 115 km, with a formal error of about 10 km and supported by depth phases. There is evidence of complexity in the source, with a secondary release of energy from the same focus after about six seconds. From original records and bulletins we establish the surface-wave magnitude (M_s as 7.4 ± 0.3, corresponding to a moment release of about 2.2 × 10²⁷ dyn.cm. The felt information is consistent with these findings, and although the earthquake was felt very widely, nowhere did it produce excessively high intensities. Our intensity assessments, usually from original sources, tend to be lower than those assigned in previous studies, the highest being IX MSK on Rhodes.     

Uncertainty Analysis of Strong-Motion and Seismic Hazard

In this article we present the modelling of uncertainty in strong-motion studies for engineering applications, particularly for the assessment of earthquake hazard. We examine and quantify the sources of uncertainty in the basic variables involved in ground motion estimation equations, including those associated with the seismological parameters, which we derive from a considerable number of strong-motion records. Models derived from regression analysis result in ground motion equations with uncertain parameters, which are directly related to the selected basic variables thus providing an uncertainty measure for the derivative variable. These uncertainties are exemplified and quantified. An alternative approach is presented which is based on theoretical modelling defining a functional relationship on a set of independent basic variables. Uncertainty in the derivative variable is then readily obtained when the uncertainties of the basic variables have been defined. In order to simplify the presentation, only the case of shallow strike-slip earthquakes is presented. We conclude that the uncertainty is approximately the same as given by the residuals typical for regression modelling. This implies that uncertainty in ground motion modelling cannot be reduced below certain limits, which is in accordance with findings reported in the literature. Finally we discuss the implications of the presented methodology in hazard analyses, which is sensitive to the truncation of the internal error term, commonly given as an integral part of ground motion estimation equations. The presented methodology does not suffer from this shortcoming; it does not require truncation of the error term and yields realistic hazard estimates. This revised version was published online in July 2006 with corrections to the Cover Date.     

Ottoman archives and the assessment of the seismicity of Greece 1456–1833

This article examines the contribution of Ottoman sources of historical information for the study of the seismicity of Greece, in particular of Athens during the period of the Ottoman domination, a period during which relatively few original Greek sources of data are available. An annotated list of a number of case histories of earthquakes in Greece from Ottoman sources is presented translating only a summary of the information for those who want to access the whole document. They contain not only a valuable record of earthquakes, but also, for the earthquake historian, a wealth of information about locations where earthquakes were not felt. The article discusses the effects of earthquakes, of the 1826–7 siege on the Acropolis its purpose being to provide information with such annotation as would facilitate its use by engineering seismologists with additional macroseismic data that could supplement the rather meagre information.     

Reappraisal of surface wave magnitudes in the Eastern Mediterranean region and the Middle East

We report on a detailed palaeomagnetic study of the Miocene Farellones volcanic formation in the Chilean Andes near Santiago (two sections, 37 sites, about 400 orientated cores). Petrological observations show evidence of low-grade metamorphism increasing downwards through the volcanic sequence. Optical observations of opaque minerals and magnetic experiments suggest that in many cases maghemitization is associated with hydrothermal alteration. However, thermal demagnetization data indicate that the low-grade metamorphism did not significantly modify the direction of the primary remanent magnetization recorded at the time of emplacement of the volcanic lava flows. Four intervals of polarity with two intermediate palaeodirections were observed in the ~650-m-thick composite section. According to the dispersion of flow average directions, palaeosecular variation was slightly larger than that observed in general during the Upper Cenozoic. The site mean directions obtained in this study differ significantly from the expected Miocene direction. Clockwise rotations of up to 20° of small blocks are probably associated with the deformation of the Andean Cordillera since middle Miocene times. Geomagnetic palaeointensity data were obtained, using the Thellier method, on 24 samples from eight distinct lava flows. The flow mean VDM varies from 1.4 to 4.0 × 10²² A m⁻². Altogether, our data seem to suggest the existence of a relatively low geomagnetic field undergoing large fluctuations. Although a linear relationship was observed between the natural remanent magnetization and the thermal remanent magnetization acquired during the Thellier–Thellier experiments, undetected chemical alteration of the magnetic minerals during hydrothermalism may also explain the unusually low palaeointensity obtained.