Estimates of vertical crustal movements along the coast of Greece,based on mean sea level data

Mean annual sea level (MASL) data for 25 Greek stations were analyzed for the time period 1969–1982. The data from 4 of these were unacceptably poor, and the record of 3 stations showed unexplained step functions that were interpreted as errors. Relative MASL between stations showed crustal stability at 10 of the 18 useful stations. The standard deviation from the long-term average of these stations was ±1.8 cm. We conclude that if station records are carefully kept in this area crustal movements in excess of 5 cm can be detected by relative MASL. A comparison of MASL data with gravity changes measured in the Peloponnese and Central Greece suggests that vertical movements occurred along a gradient equal to or larger than the free air gradient. We conclude that the gravity network should be reoccupied frequently such that the non-tectonic effects to be determined from the probable observed gravity changes, and the tectonic vertical movements may be better understood. A co-seismic subsidence of about 5 cm is inferred to have taken place near Korinth during the 1981,M _s =6.8, earthquake, which occurred 20 km N of this tide gauge (Posidonia). During 2.5 years before the 1968 Thessaloniki,M _s =6.6, earthquake, sea level was lower than average suggesting possible crustal elevation of 3.6 cm at about 28 km epicentral distance. Because of the small amplitude of this change we are not certain that it represents crustal uplift. At station Myrina (on Limnos) a strong and consistent trend of subsidence accumulated a 15 cm change between 1975 and 1980. Chios showed a trend of emergence (total accumulation about +5 cm), while Volos showed a trend of subsidence (approximately ?5 cm total). Kefalinia appears to have subsided about 10 cm during the data period. The six stations along the Hellenic arc plate boundary showed nearly constant MASL, suggesting that crustal stability existed there during the last 14 years. We conclude that MASL data in Greece can be useful for understanding tectonic processes, especially if these data are gathered carefully and at numerous locations, and are cross-correlated to high precision repeat gravity measurements, and geodetic releveling. Also, MASL data on active volcanic islands have excellent potential for detecting uplift before future eruptions.     

Die Laufzeitfunktion in der Reflexionsseismik des quasi Einachsig inhomogenen Körpers

Zusammenfassung Es wird die Laufzeitfunktion (Reflexionsseismik) für einen quasi einachsig inhomogenen Körper berechnet und zwei einfache Beispiele und ihre Anwendungen behandelt.

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Summary The travel-time function (reflection seismic) for a quasi uniaxial inhomogeneous medium is calculated and two simple examples are given.

     

Das ebenen-Schichtenproblem der Reflexionsseismik mit konstanten Frontgeschwindigkeiten,beliebigen Neigungen und beliebiger Lage der Quelle

Zusammenfassung Es wird das ebenen-Schichtenproblem der Reflexionsseismik mit konstanten Frontgeschwindigkeiten, beliebigen Neigungen und beliebiger Lage der Quelle allgemein behandelt und durch Verallgemeinerung der tt Methode ein einfaches Aufschlussverfahren für geneigte Schichten entwickelt.

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Summary The two-dimensional problem of the reflection seismic with arbitrary inclined surfaces of discontinuity, const. wave-velocities and an arbitrary position of the source is generally treated. Finally a tt method for inclined layers is outlined.

     

Ergebnisse der Registrierungen der Zahl der Kondensationskerne in Basel und seiner nächsten Umgebung

Zusammenfassung In Fortsetzung früher mitgeteilter Ergebnisse von Registrierungen mit demVerzár'schen Kernzähler in Basel wird der Einfluss der Luftmassenwechsel, des Sonnenscheins und der Niederschläge auf den Kerngehalt untersucht. Weiterhin werden die Ergebnisse gleichzeitiger Registrierungen im Stadtinnern und am Stadtrand, sowie am Stadtrand und einem Villenvorort eingehend diskutiert.Ein weiterer Vergleich zwischen Basel und Payerne ergibt Beziehungen zwischen den Tagesmitteln der Kernzahlen dieser fast 100 Km von einander entfernten Orte.

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Summary Continuing previously communicated results of recordings with theVerzár nuclei counter at Basle the influences of changes of air masses, of sunshine and precipitation on nuclei concentration are studied. Furthermore the results of simultaneous recordings in the centre of the city and on the outskirts, as well as on the out-skirts of the city and at a near-by village are thoroughly discussed. A further comparison between Basle and Payerne shows connections between daily means of nuclei concentration of these two towns, which are about 100 Km apart.

     

Die Bestimmung einer beliebig gekrümmten Schichtgrenze aus seismischen Reflexionsmessungen

Zusammenfassung Es wird dargelegt wie man eine beliebig gekrümmte Schichtgrenze aus seismischen Reflexionsmessungen längs einer beliebig gekrümmten Messfläche berechnen kann. Dazu wird vorausgesetzt, dass die Flächez=f(x,y), die die Schichtgrenze darstellt und die Messflächez=(x,y) zusammen eine glatte geschlossene Fläche bilden und, dass das eingeschlossene Material homogen und isotrop ist.

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Summary Under the assumption that the measuring surfacez=(x,y) and the reflection horizon of a structurez=f(x,y) have an arbitrary curvature a simple method is developed for calculating the surfacef from seismic reflection data measured along the surface . In addition the general solution is discussed and some special cases are treated.

     

Scenarios of Seismic Risk in the United Arab Emirates,an Approximate Estimate

We estimate the losses due to 10 scenario earthquakes in 150 settlements of the United Arab Emirates (UAE). For southern Iran, we use four source zones and the maximum magnitudes in them as determined by GSHAP (7.2 M 8.1). For six local scenario earthquakes, we use the range 5.5 M 6.5, place the sources mainly on mapped faults and vary the distance to major cities from 10 to 60 km. In the test case of the Masafi earthquake (M5, 11 March 2002), the method and data bank we use yield the correct results, suggesting that our approach to the problem is valid for the UAE. The sources in Iran are expected to cause only minor damage, except for an M8.1 earthquake in the Makran region. For such an event we expect some deaths, several hundred injured and a loss of 3–6% of the value to the building stock in the northeastern UAE, including Oman. The losses for local scenarios with epicenters in the unpopulated areas of the UAE and for scenarios with M < 5.8 are estimated to be minor. Because the two major mapped faults run through several of the large cities, scenarios with short epicentral distances from cities have to be considered. Scenarios with M6 near cities lead to estimates of about 1000 ± 500 deaths, and several thousand injured. Most buildings are expected to be damaged to a moderate degree and the loss to buildings is estimated around 1/4of their value. If the magnitude should reach 6.5, the losses to humans and to building value could be staggering. These estimates are approximate because: (1) there exists no local seismograph network that could map active faults by locating microseismicity; (2) there exist no historically old buildings that could serve as tests for effects due to strong ground motion in the past; (3) there exist no microzonation of the subsurface properties in this region of unconsolidated building ground; (4) there exist no detailed inventory of building fragility. Nevertheless, our conclusion that there exists a substantial seismic risk in the UAE is reliable, because our method yields accurate results in the cases of earthquakes with known losses during the last several decades in the Middle East.