Correlation of MLH and mpv by Data of the Network of Seismic Stations of the U.S.S.R.

2,591

1,234

Examination of more than 100 fault plane solutions for earthquakes within the Alpide belt between the Mid-Atlantic ridge and Eastern Iran shows that the deformation at present occurring is the result of small continental plates moving away from Eastern Turkey and Western Iran. This pattern of movement avoids thickening the continental crust over much of Turkey by consuming the Eastern Mediterranean sea floor instead. The rates of relative motion of two of the small plates involved, the Aegean and the Turkish plates, are estimated, but are only within perhaps 50 per cent of the true values. These estimates are then used to reconstruct the geometry of the Mediterranean 10 million years ago. The principal difference from the present geometry is the smooth curved coast which then formed the southern coast of Yugoslavia, Greece and Turkey. This coast has since been distorted by the motion of the two small plates. Similar complications have probably been common in older mountain belts, and therefore local geological features may not have been formed by the motion between major plates.A curious feature of several of the large shocks for which fault plane solutions could be obtained for the main shock and one major aftershock was that the two often had different mechanisms. 113 20 40 60 FIG. 3. Epicentres of foci at and below 50 km between 1961 and 1970. The depth of the foci given by the USCGS were used to obtain this figure, and may well be in error by 50 km. Since focal depths of greater than 50 km are believed to occur only where plates are being destroyed, the activity in this figure suggests that crustal shortening is now taking place over a wide region in the Eastern Mediterranean and South-west Asia. * Dielines of Figs 1 and 9 at a scale of 1:12 233 OOO, Figs 15-18 at 1: 1 million and Figs 24, 25, 29 and 3 1 at 1 :2.5 million can be provided at cost.

Section: The Aegean and Surrounding Regionsmentioning

confidence: 81%

Active Tectonics of the Mediterranean Region

McKenzie¹

1972

2,591

1,234

“…However, their corrections cannot be compared with those from other studies as they have been calculated with respect to a zero station correction for Obninsk (OBN). The same applies for the station corrections determined by Bune et al (1970) for the major seismographic stations in the former USSR.…”

Section: Introductionmentioning

confidence: 90%

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

Ambraseys

Douglas

2000

There have been many attempts to improve parametric catalogues for surface wave magnitudes for earthquakes of this century, and many of these attempts have been based on empirical adjustments to homogenize and complete catalogues without recourse to the instrumental data with which these magnitudes have been calculated. Using the Prague formula with station corrections and a substantial volume of amplitude and period readings of surface waves, culled from station bulletins, we calculated uniformly the magnitude of all significant earthquakes, 1519 in all, in the Eastern Mediterranean region and in the Middle East between 1900 and 1998. We also calculated station corrections and their variation with time, and examined the effect of distance adjustment of the Prague formula on M(s) estimates. We find that the current procedure of averaging station magnitudes underestimates M(s). This underestimation depends on the variance and on the number of station magnitudes available for the calculation of M(s), which can be as large as 0.3 magnitude units or more. We also find that station corrections have a rather small overall effect on event magnitude, of less than +0.1, except when the number of observing stations is small, in which case the correction may reach +0.3 magnitude units. Event magnitudes derived from station magnitudes with distance adjustment, calculated from the original Prague formula, are on average 0.1 units larger than M(s) without distance correction. We find that for shallow events, Gutenberg's estimates are, on average, larger by 0.12 units and show a significant scatter, with a standard deviation three times the mean value. We find similar differences and scatter for surface wave magnitudes estimated by other workers and agencies

“…

In a recent paper (Bune et al 1970), a comparison of USSR and NOS (formerly C & GS) values was made and suggestions given for modifying NOS procedures. The paper also pointed out some of the problems of magnitude determination.

…”

mentioning

confidence: 99%

“…It is the intention of this communication to examine items raised in the Bune, et al (1970) paper and other more relevant aspects of magnitude determination. As a first step in this direction, we present a comparison of the USSR network data taken from trimonthly bulletins and the NOS data taken from PDE reports.…”

mentioning

confidence: 99%

A Comparison of NOS and USSR Magnitudes

Jordan¹,

Hunter²

1972

In a recent paper (Bune et al. 1970), a comparison of USSR and NOS (formerly C & GS) values was made and suggestions given for modifying NOS procedures. The paper also pointed out some of the problems of magnitude determination. We would like to present some of our data and make appropriate comments.Computation of body wave (mb) magnitudes by NOS was initiated in February 1963 with the use of Gutenberg & Richter's (1956) formula: A = ground amplitude in microns, recorded on short-period, vertical component instruments, T = period in seconds, and Q = distance/depth calibration factor. Since then, the NOS has computed over 25000 magnitudes. Contrast this with Gutenberg & Richter (1954) who used less than 1000 earthquakes to cover worldwide seismicity.It is the intention of this communication to examine items raised in the Bune, et al. (1970) paper and other more relevant aspects of magnitude determination. As a first step in this direction, we present a comparison of the USSR network data taken from trimonthly bulletins and the NOS data taken from PDE reports.To determine the relative capability of the two networks, a simple count of located events was made for the June to August 1968 period. The total of 1798 events consists of 1390 located by the NOS only, 383 located by both networks, and 25 located by USSR only. The NOS located over four times as many events as the USSR (1773, NOS; 408, USSR), a result which is to be expected based on the relative size and distribution of stations in the two networks. A comparison of magnitudes determined by the two systems is somewhat less direct, since the USSR reports only M surface-wave magnitudes determined from long-period horizontal instruments, whereas the NOS reports both body wave (mb) and, more recently, surface-wave magnitudes (Ms), also from long-period horizontal instruments but of a different type than the USSR seismographs.Two different approaches to the comparison have been made. For the first of these, the International Seismological Centre (ISC) Bulletin for 1964 was used as a data source, since it lists both NOS and USSR values for the reported events. Figs 1 to 4 show plots of magnitude residuals, USSR (M) values minus NOS (m,,) values, for various areas. Mean magnitude residuals and standard deviations * NOS Seismology staff transferred to Earth Sciences Laboratories of NOAA! Environmental