The statistics of large earthquake magnitude and an evaluation of Greek seismicity

SIGLEAvailable from British Library Document Supply Centre- DSC:D71984/87 / BLDSC - British Library Document Supply CentreGBUnited Kingdo

Seismic risk of circum-pacific earthquakes I. Strain energy release

Commonly used earthquake "whole process" frequency - magnitude and strain energy - magnitude laws are merged to obtain an analytic expression for an upper bound magnitude to regional earthquake occurrence M3, which is expressed primarily in terms of the annual maximum magnitude M1 and the magnitude equivalent of the annual average total strain energy release M2. Values of M3 are also estimated graphically from cumulative strain energy release diagrams. Both methods are illustrated by application to the high seismicity of the circum-Pacific belt, using Duda's (1965) data and regionalisation. Values of M3 obtained analytically, with their uncertainties, are in agreement with those obtained graphically. Empirical relations are then obtained between M1, M2, and M3, which could be of general assistance in regional seismic risk considerations if they are found to be of a universal nature. For instance. M3 and M2 differ by one magnitude unit in subregions of the circum-Pacific. © 1983 Birkhäuser Verlag

Greek tectonics and seismicity

The validity of existing tectonic models for the area of Greece is examined in the light of the new recalculated parameters for earthquakes of the region (Makropoulos and Burton, 1981). Relocated hypocentral positions are extracted from the catalogue to form radial and vertical distance-depth cross-sections centred on a reference point near the mid-point of the Aegean Volcanic arc, and these are used to form a three dimensional topography of the base of earthquake occurrence below 60 km. Isodepth maps are extracted from this topography as both three and two dimensional map presentations. These maps reveal several significant features of deep-seated tectonic processes in the region. Isodepths exceeding 150 km are seen in the northwest Aegean, and these are more closely linked to the Sporadhes and Gulf of Thermaicos, rather than the North Aegean trough. The 150 km isodepths are also seen in the northeast Aegean straddling the Dardanelles; in the northeastern part of the Peloponnesus, Gulf of Saronikos and eastern Gulf of Corinth in the southern Peloponnesus towards Crete; and extending from north of Kos to south of Rodos. The largest extent of deepest activity is seen south of Rodos and this continues towards southwest of Turkey. The subduction zone of the Hellenic arc is clear, but smooth Benioff zones are not the norm, and these data show that structural complexity is more readily observed. It is concluded that none of the proposed tectonic models completely explain the observed activity over the whole area, and rather than propose yet another model places where further work is still particularly necessary are identified. © 1984

Hazan: a FORTRAN program to evaluate seismic-hazard parameters using Gumbel's theory of extreme value statistics

A FORTRAN IV computer program for seismic Hazard Analysis is presented and illustrated by an example. It evaluates the parameters of Gumbel's first and third type asymptotic distributions of extreme values and in the latter situation it is based on the nonlinear least-squares method developed by Marquardt. The application of this method is developed here so that the uncertainty on each parameter of Gumbel's third distribution is estimated and the complete covariance matrix is obtained, in recognition of the importance of assigning uncertainties to all parameters used for seismic hazard assessment. The primary data required is a chronological catalogue of earthquake magnitudes, however, earthquake magnitude or a related value of earthquake caused ground acceleration, velocity, or displacement may be the quantity used in the ensuing analysis to characterize the seismic hazard. © 1986

Seismic risk of circum-pacific earthquakes I. Strain energy release

Commonly used earthquake "whole process" frequency - magnitude and strain energy - magnitude laws are merged to obtain an analytic expression for an upper bound magnitude to regional earthquake occurrence M3, which is expressed primarily in terms of the annual maximum magnitude M1 and the magnitude equivalent of the annual average total strain energy release M2. Values of M3 are also estimated graphically from cumulative strain energy release diagrams. Both methods are illustrated by application to the high seismicity of the circum-Pacific belt, using Duda's (1965) data and regionalisation. Values of M3 obtained analytically, with their uncertainties, are in agreement with those obtained graphically. Empirical relations are then obtained between M1, M2, and M3, which could be of general assistance in regional seismic risk considerations if they are found to be of a universal nature. For instance. M3 and M2 differ by one magnitude unit in subregions of the circum-Pacific. © 1983 Birkhäuser Verlag

Seismic hazard in Greece. I. Magnitude recurrence

Two different methods are applied to the earthquake catalogue for Greece (Makropoulos and Burton, 1981), MB catalogue, to evaluate Greek seismic hazard in terms of magnitude: earthquake strain energy release and Gumbel's third asymptotic distribution of extreme values. It is found that there is a close relationship between results from the two methods. In places where the cumulative strain energy release graphs include at least one well defined cycle of periodicity of strain release, then the parameters of the third type asymptote are well defined with small uncertainties. In almost all cases the magnitude distribution shows a remarkably good third type asymptotic behaviour. The results are presented in the form of graphs and contour maps of annual and 80-year modes, and magnitudes with 70% probability of not being exceeded in the next 50 and 100 years. For six of the most heavily industrial and highly populated centres of Greece magnitude hazard parameters are also derived and examined in more detail, thereby illustrating the direct applicability of the methods in terms of zoning. The close agreement between observed and predicted extreme magnitudes shows that the sample period considered (1900-1978), is long enough to obtain statistically stable estimates. For Athens the upper bound magnitude is found to be 6.7 ± 0.3 (within 100 km) and 6.8 ± 0.4 (100 km) from the two methods respectively, whereas for Corinth an earthquake of magnitude 6.5 has a mean return period of 43 years. Greece as a whole has an upper bound magnitude 8.7 ± 0.6 and earthquakes of a size similar to the 1903 Kithira event (M ≈ 8.0) have a mean return period of about 200 years. The significantly different maps contouring magnitudes of the annual and 80-year modes result from the fact that each place has its own distribution curvature for magnitude occurrence, and thus they are not a linear extrapolation of each other. However, as longer return periods are considered, these differences become small because the expected magnitudes approach the regional upper bound. A feature common to all these maps is the existence of three well defined aseismic blocks: 1. (a) the Attikocycladic block 2. (b) the Ptolemais basin and 3. (c) the block formed by the northeastern part of Greece. Well defined areas of high seismic hazard which correlate with the most tectonically active areas are: 1. (a) along the Hellenic arc: the Greek-Albania border, Leukas-Cephalonia Islands and the southeastern end of the arc 2. (b) the western end of the North Anatolian fault and 3. (c) the Chalkidiki peninsula and the northern Sporadhes Islands. © 1985

Seismic hazard in Greece. I. Magnitude recurrence

Two different methods are applied to the earthquake catalogue for Greece (Makropoulos and Burton, 1981), MB catalogue, to evaluate Greek seismic hazard in terms of magnitude: earthquake strain energy release and Gumbel's third asymptotic distribution of extreme values. It is found that there is a close relationship between results from the two methods. In places where the cumulative strain energy release graphs include at least one well defined cycle of periodicity of strain release, then the parameters of the third type asymptote are well defined with small uncertainties. In almost all cases the magnitude distribution shows a remarkably good third type asymptotic behaviour. The results are presented in the form of graphs and contour maps of annual and 80-year modes, and magnitudes with 70% probability of not being exceeded in the next 50 and 100 years. For six of the most heavily industrial and highly populated centres of Greece magnitude hazard parameters are also derived and examined in more detail, thereby illustrating the direct applicability of the methods in terms of zoning. The close agreement between observed and predicted extreme magnitudes shows that the sample period considered (1900-1978), is long enough to obtain statistically stable estimates. For Athens the upper bound magnitude is found to be 6.7 ± 0.3 (within 100 km) and 6.8 ± 0.4 (100 km) from the two methods respectively, whereas for Corinth an earthquake of magnitude 6.5 has a mean return period of 43 years. Greece as a whole has an upper bound magnitude 8.7 ± 0.6 and earthquakes of a size similar to the 1903 Kithira event (M ≈ 8.0) have a mean return period of about 200 years. The significantly different maps contouring magnitudes of the annual and 80-year modes result from the fact that each place has its own distribution curvature for magnitude occurrence, and thus they are not a linear extrapolation of each other. However, as longer return periods are considered, these differences become small because the expected magnitudes approach the regional upper bound. A feature common to all these maps is the existence of three well defined aseismic blocks: 1. (a) the Attikocycladic block 2. (b) the Ptolemais basin and 3. (c) the block formed by the northeastern part of Greece. Well defined areas of high seismic hazard which correlate with the most tectonically active areas are: 1. (a) along the Hellenic arc: the Greek-Albania border, Leukas-Cephalonia Islands and the southeastern end of the arc 2. (b) the western end of the North Anatolian fault and 3. (c) the Chalkidiki peninsula and the northern Sporadhes Islands. © 1985

Hazan: a FORTRAN program to evaluate seismic-hazard parameters using Gumbel's theory of extreme value statistics

A FORTRAN IV computer program for seismic Hazard Analysis is presented and illustrated by an example. It evaluates the parameters of Gumbel's first and third type asymptotic distributions of extreme values and in the latter situation it is based on the nonlinear least-squares method developed by Marquardt. The application of this method is developed here so that the uncertainty on each parameter of Gumbel's third distribution is estimated and the complete covariance matrix is obtained, in recognition of the importance of assigning uncertainties to all parameters used for seismic hazard assessment. The primary data required is a chronological catalogue of earthquake magnitudes, however, earthquake magnitude or a related value of earthquake caused ground acceleration, velocity, or displacement may be the quantity used in the ensuing analysis to characterize the seismic hazard. © 1986

Rates of crustal deformation in the Gulf of Corinth (central Greece) as determined from seismicity

Seismic moment values and fault plane solutions for large (Ms ≥ 5.5) earthquakes which occurred in the Gulf of Corinth (central Greece) over the last 25 years, were used to calculate the average rate of deformation in the area. The results show north-south and east-west extension together with a downward movement of the northern side of the Gulf relative to the south at about 1 mm/yr. © 1986