Seismotectonics and the earthquake frequency-magnitude distribution in the Aegean area

Abstract

A study of Aegean seismotectonics and the resulting frequency-magnitude distribution on a broad scale is undertaken, using the tectonic model of Le Pichon & Angelier. This implies a tectonic moment release rate due to the spreading of the Aegean of 17 f 8 x 10'' N m-' yr-' over the past 13 Ma, if stretching is due mainly to a series of normal faults dipping at about 45" in a seismogenic crust 10-20km deep. The moment-magnitude relation from an instrumental magnitude catalogue is log M, = A + Bm, with A = 10.970 f 0.294, B = 1.206 in SI units. This is established from 50 events of magnitude M, > 5.3 whose scalar seismic moments M, have been evaluated in a homogeneous manner for the region by spectral analysis of surface waves at 30-60 s period. By contrast published body-wave analyses, from waveform modelling at 20s period and moment tensor analyses seem to produce seismic moments which are lower by a factor of two or so on average. This moment-magnitude relation implies a seismogenic moment release rate due to stretching in the Aegean of 14 x 10l8 N m-l yr-' during the time period 1918-81 and 17 X 10l8 N m-l yr-' for the period 1964-81, within a factor of two or so uncertainty. This implies that the energy release in the brittle crust due to Aegean spreading is substantially seismic within the stated accuracy, and is also relatively stationary even when compared with the tectonic moment release rates. A similar comparison using the same tectonic model shows that the subducting slab is sinking beneath the Hellenic arc almost completely aseismically, and that processes such as near vertical slab pull and confined thermal expansion could explain most of the observed seismic energy release by internal deformation of the slab. The frequency-magnitude statistics for the area of active extension has a characteristic earthquake of magnitude 7M,, corresponding approximately to fault depths of 10-14 km for an aspect ratio of 2 and a strain drop of lop4. This is close to the observed seismogenic depth (10-20 km) for well-determined earthquakes in the Aegean area.

Generalized statistical mechanics approaches to earthquakes and tectonics

“…The authors maximized entropy to derive a probability density function of earthquake magnitudes p(M) that has the form of a truncated exponential distribution: 15) where m 1 is the minimum magnitude in the dataset and β the Lagrange multiplier. Furthermore, Main & Burton [75] maximized entropy using the constraints of the average magnitude m and the average seismic energy release E to derive a gamma distribution of earthquake energies p(E), consisting of a power-law distribution at small magnitudes that corresponds to the G-R scaling relation (equation (2.4)) and an exponential (Boltzmann) tail at larger magnitudes:…”

Law for the distance between successive earthquakes

“…It can be formulated by the maximum entropy principle. Previously, in seismology, maximum entropy principle was examined for describing, for example, the frequency-magnitude distribution [Main and Burton, 1984], in which the ordinary Boltzmann-GibbsShannon entropy was employed. Here the entropy functional to be considered is a generalized one termed the Tsallis entropy.…”

Slip on ridge transform faults : insights from earthquakes and laboratory experiments

“…The upper limit of the scaling region is specified by a magnitude cutoff mc or an equivalent moment cutoff Mc, representing the "outer scale" of fault rupture. A variety of truncated GR distributions are available [Molnar, 1979;Main and Burton, 1984;Kagan, 1991Kagan, , 1993Kagan and Jackson, B12302 BOETTCHER AND JORDAN: TRANSFORM FAULT SEISMICITY B12302 2000; Kagan, 2002a1, but they all deliver a scaling relation of the form EM IX M;-~.…”