Stathis C. Stiros

Earthquake clustering in the eastern Mediterranean during historical times

Most coastal sectors which show evidence of Holocene coseismic uplift in Greece and the Eastern Mediterranean were raised during a short period called here the Early Byzantine tectonic paroxysm (EBTP) between the middle of the fourth and the middle of the sixth century A.D. The areas uplifted at that time include Cephalonia and Zante in the Ionian Islands, Lechaion and the Perachora Peninsula in the Gulf of Corinth, the Pelion coast of Thessaly, Antikythira and the whole of western Crete, a coastal sector near Alanya in southern Turkey, and the entire Levant coast from Hatay (Turkey) to Syria and the Lebanon. The amount of the EBTP uplift was generally between 0.5 m and 1.0 m but reached a maximum of about 9 m in southwestern Crete. In several areas (Zante, Pelion coast, Antikythira, western Crete, Alanya), the EBTP uplifted shoreline is the only evidence of Holocene emergence. In other areas, however, a similar uplift occurred earlier in the Holocene (Levant coast), or more recently (Cephalonia). Evidence of preseismic subsidence prior to the EBTP uplift has been reported from Thessaly, Antikythira, and Crete ; in both the latter islands, the EBTP uplift was preceded by a series of about 10 coseismic small subsidence movements, each measuring some tens of centimeters, which took place in the preceding 3000 years. No evidence was observed of postseismic vertical displacements.

Episodic uplift deduced from Holocene shorelines in the Perachora Peninsula, Corinth area, Greece

Four raised shorelines, between +1.1 m and +3.5 m, have been identified at two localities on the Perachora Peninsula and were dated by AMS 14C to between 6400 and 1500 calibrated years ago. Uplift movements seem to have occurred in increments of 0.8 ± 0.3 m, with a return period of about 1600 years. The last uplift coincided with a regional tectonic paroxysm, which has already been documented in several areas of the eastern Mediterranean. The average uplift rate was probably faster during the Holocene than the average since the Last Interglacial period. No important vertical displacement occurred in this area at the time of (or after) the 1981 earthquake, but a new episode of coseismic uplift may be in preparation.

Experimental Assessment of the Accuracy of GPS and RTS for the Determination of the Parameters of Oscillation of Major Structures

Based on experimental evidence, the authors explore the possibility of using GPS and robotic total stations (RTS) for measurements of oscillations of relatively rigid structures (modal frequencies up to 3–4 Hz). The strategy was to compare uni-axial oscillations of known characteristics with simultaneous recordings of both GPS and RTS, and analyze obtained time series to determine amplitude and frequency of oscillations. The conclusion of this study is that GPS can record oscillations up to 4 Hz with a minimum amplitude of 5–10 mm with an accuracy of a few millimeters, and that RTS can record peak oscillations with submillimeters to a few millimeters accuracy, but at high frequencies some cycles were lost. Based on recordings of both instruments, frequencies of oscillations were also accurately determined, though noise seems to increase with increasing frequency. Spectral analysis was based on least-square-based software which permits one to analyze discontinuous, short, and non-equispaced time series. The latter derive either from GPS signal outages and hardware/software imperfections, or from a non-constant rate of sampling for RTS. The overall conclusion is that the adopted computational approaches permit some main disadvantages of these instruments to be overcome and also allow conventional GPS and RTS instrumentation to be used for a wide range of cases of structural monitoring, especially if displacements relative to an independent coordinate system are required.

Subsidence of the Thessaloniki (northern Greece) coastal plain, 1960–1999

Comparison of aerial photos, maps and triangulation data reveal that in the last 40 yr a part of the Thessaloniki coastal plain, a delta formed in the last 2500 yr, subsided at a rate of up to 10 cm/yr. As a consequence the sea invaded up to 2 km inland; precious land in the suburbs of the city was lost, while a village and major industrial plants are in risk of flooding. Part of the land was reclaimed thanks to barriers, pumping and artificial raising of the land surface. Yet, the situation is unstable and flooding is not unusual. Ground water withdrawal for the needs of the Thessaloniki metropolitan complex has initially been regarded as the cause of the subsidence. However, the lack of correlation in space and in time between fluctuations of piezometric levels, topographic changes and pumping indicates that the observed subsidence should be regarded as the cumulative effect of several factors, including consolidation of near-surface sediments due to the decline of the piezometric level and the partial abandonment of the delta, oxidation of peat soils in the vadose zone, synsedimentary deformation (faulting and flow) and loading-induced consolidation of deeper sediments.

Coastal uplift, earthquakes and active faulting of Rhodes Island (Aegean Arc): modeling based on geodetic inversion

The geodetic inversion technique was used to model the fault pattern responsible for the uplifted Holocene notches along the NE Rhodes Island coast (SE edge of the Hellenic (Aegean) Arc). Input in the modeling was the elevation of uplifted notches, up to 6000 yr old, which are interpreted to reflect remains of fossil shorelines, to testify to a series of earthquakes producing both uplift and subsidence (i.e. to elastic dislocations) and to correspond to geodetic data senso lato. These shorelines, up to 3.8 m high, were probably originally continuous along the whole of the 75-km-long SE Rhodes coast, possibly locally disturbed by minor normal faults, and reflect the last phases of the uplift and tilting of the island as a rather rigid block since Late Pliocene. Their radiocarbon dating was further refined from archeological data testifying to an about 1-m subsidence associated with the 227 BC earthquake, followed by >3-m seismic uplift. Inversion, constrained by the hypothesis of a compressional fault offshore Rhodes, was based on standard, uniform-slip, elastic dislocation analysis; it proved to depend only weakly even on extreme glacio-isostatic corrections and indicated that coastal uplift is dominated by a main compressional fault zone offshore, sub-parallel to the island coast, with normal faults inland reflecting thin-skin tectonics. This fault pattern, similar to that of western Crete, is confirmed by seismic reflection profiles indicating a major reverse close to the modeled fault and can explain (1) the occurrence of strong (M>7.5) historical earthquakes producing tsunamis and destruction on an East Mediterranean scale, (2) the alternation of uplift and subsidence as a result of fault shift inside the same fault zone, and (3) the long-term uplift of the island as a rather conjugate effect of the formation of an about 4.5-km-deep, 5-Myr-old marine basin SE of Rhodes, bounded to the NW by the modeled fault zone. The seismic risk of Rhodes, higher in its NE part of the island and than what was previously believed, is associated with strong (M>7.5) earthquakes producing widespread destruction, tsunamis, coastal uplift and coastal subsidence.

Measuring Deflections of a Short-Span Railway Bridge Using a Robotic Total Station

AbstractA robotic total station (RTS) [or robotic theodolite or theodolite positioning system (TPS)] was used for the first time to measure the deflections of a short-span bridge in response to passing trains. The RTS measurements aimed to a reflector which was set on one of the midspans of the historical Gorgopotamos Bridge in Greece permitted to identify the measurement noise (apparent displacements) up to ±1.3 mm when no trains were passing, and deflections with peaks of 2.5–6 mm during intervals when small or larger trains were passing. These results confirm previous experiments and indicate that, under certain conditions (mostly favorable atmospheric conditions), an RTS can be used for monitoring dynamic displacements of relatively stiff bridges, and as a useful tool for structural health monitoring.

Late holocene coseismic vertical displacements and tsunami deposits near Kynos, Gulf of Euboea, Central Greece

Abstract Marine bioerosion marks and radiocarbon AMS dating give evidence of a two-phase sequence of coseismic vertical displacements which occurred during the Late Holocene in the Livanates-Arkitsa area (south coast of the Euboea Gulf). Morphological and biological arguments suggest that both the displacements were superimposed on a gradual relative sea-level rise. The earlier coseismic movement (a subsidence of 0.9 m max.) is possibly related to a tsunami wave, dated between 1380 and 965 B.C., which swept at 16 m in altitude the nearby archaeological site of Homeric Kynos. The later coseismic movement, between 360 B.C. and A.D. 210, was an uplift greater than 1.4 m.

Quaternary deformation of the Isthmus and Gulf of Corinthos (Greece)

Interdisciplinary data suggest that the Quaternary, late Holocene, and present-day deformation patterns of the Isthmus of Corinthos, Greece, are very similar and can be compared to a platelike body under torsion. This hypothesis is consistent with the vertical differential motions observed in the adjacent Corinthiakos Gulf. A possible explanation is that the back-arc compressional zone is much wider than formerly believed and extends to an area of normal faulting, parallel to the direction of the compression. This stress field produces a central bulging in the southern coast and a depression in the northern coast of the Corinthiakos Gulf; the easternmost ends of this depression and bulging are the southern and northern parts of the isthmus, tilted to the east and to the west, respectively.

Seismicity of Western Crete and the destruction of the town of Kisamos at AD 365: Archaeological evidence

The study of numerous archaeological excavations permits us to concludethat shortly after AD 355–361, the wealthy Roman town of Kisamos inwestern Crete was affected by a devastating earthquake (minimum intensityXI), which left many of the towns inhabitants buried under the ruins. Thisearthquake can be related to the July 21, 365 earthquake (M > 8),which was associated with a great tsunami, and was probably responsible forup to 9 m uplift of Western Crete; it probably resulted from thereactivation of a major thrust fault along the Hellenic Arc. Thearchaeological stratigraphy of Kisamos between circa AD 50 and AD650 testifies to two other, small-scale stratigraphic discontinuities that maybe related to two other smaller earthquakes, which produced 10–20 cmof coastal subsidence in AD 46–66 and in circa AD 270. There isevidence for a tsunami associated with the AD 46–66 earthquake, whichagrees with sedimentological data from the nearby ancient harbour ofPhalasarna, which was uplifted about 6.5 m in AD 365.The following evidence indicates that Western Crete is not seismicallyquiescent, as previously believed on the basis of historical data, but that ithas been affected by very strong, AD 365-type earthquakes followed byrelatively quiescence periods, that were at least several thousand years long:(1) Major earthquakes of Western Crete produced coastal uplift orsubsidence, while coastal stability indicates the absence of strongearthquakes; such stability characterizes this part of the island after AD365; (2) No evidence of earthquakes exist in the archaeological record ofKisamos between AD 365 and circa AD 650 and of Chania since AD1400/1500.

Predictions and observations of convergence in shallow tunnels: case histories in Greece

Abstract Convergence of shallow tunnels (30–120 m overburden thickness) constructed in Greece in different types of rock masses has been assessed as a function of the Geological Strength Index (GSI classification). Predictions of maximum vertical and horizontal convergence, during or shortly after tunnel excavation, were made using Finite Element Modeling (FEM) and the ‘characteristic line’ theory, and were found to be in good agreement with geodetic observations of convergence collected during a period of approximately 2 months after the section excavation. The results from FEM were found to adequately and reliably predict the expected deformation during tunnel excavation. The theory of the ‘characteristic line’, on the other hand, seems to offer a realistic and reliable upper-bound estimate of the convergence.