Nonlinearity of the magnitude‐frequency relation in the Hellenic Arc‐Trench System and the characteristic earthquake model

Abstract

Magnitude‐frequency (G‐R) relations of shallow mainshocks have been examined in five separate segments of the Hellenic Arc‐Trench (HA‐T) system, in its western and eastern megasegments as well as in the HA‐T system considered as an entity. Data sets of Ms ≥ 4.5 and Ms ≥ 6.0 covering the 22‐year and 85‐year intervals of 1964–1985 and 1901–1985, respectively, have been used. Frequencies of the 22‐year interval have been normalized to the 85‐year interval so that to obtain frequencies N compatible with the real frequencies, Nr, of the 85‐year interval for magnitudes of Ms ≥ 6.0. Straight G‐R lines determined for N of small and moderate shocks as a rule do not fit, when extrapolated, the larger magnitude frequencies N and Nr. Magnitude gaps, bulge effects, and trends toward the vertical are the geometrical expressions of the nonlinear structure of G‐R in the large magnitude range. Magnitude gaps ranging from 0.5 to 0.9 in the Nr plots and in a wider magnitude spectrum in the N plots, of four out of five separate segments, indicate that the stress fails to release with ruptures of moderate size, thus implying that the characteristic earthquake model may provide an adequate explanation for the G‐R nonlinearity. The Ionian Islands segment constitutes an obvious exception. No magnitude gap in Nr appears and the G‐R linearity is well shaped. Characteristic events may not occur in that segment. When two or more segments are examined together as megasegments, the magnitude gap disappears because of overlapping of separate gaps. The nonlinear structure of G‐R shows the general need for properly designed models of seismic hazard determination.

The Lefkada, Sea (Greece), shock (Mw 6.2) of 14 August 2003: Evidence for the characteristic earthquake from seismicity and ground failures

“…G-R relationships for segments of the Hellenic Arc-Trench system showed that deviations from linearity could be explained by the characteristic earthquake model with the Ionian Islands segment being a possible exception (Papadopoulos et al, 1993). However, this exception may be only apparent due to that the examination was made for the ensemble of earthquakes sampled without regard to specific fault segments.…”

The Cephalonia, Ionian Sea (Greece), sequence of strong earthquakes of January-February 2014: a first report

“…1,[3][4][5] There is evidence that the seismicity of the Ionian segment of the Hellenic Arc, including Cephalonia Isl., does not fit the characteristic earthquake model, as the rest segments of the Hellenic Arc do. 6 Possibly this is due to that the interaction between CTFZ and western Hellenic subduction complicates the seismotectonics and controls the seismic coupling of the area. 7,8 Therefore, the study of the 2014 earthquakes is expected to help substantially in understanding better the seismotectonics and geodynamics of the Ionian segment of the Hellenic Arc.…”

The Probability of Strong (M≥7.5) Earthquakes in Fault Zones of Central Asia (Tectonophysical Analysis)

“…В работе [Sherman et al, 2003] показано, что изменение фи-зики очага разрушения (землетрясения) происхо-дит на границе магнитуд М=5.5-6.5. Похожие зна-чения были получены в работах [Pacheco et al, 1992;Papadopoulos et al, 1993;Ulomov, 1999], в ко-торых авторы отмечают, что изменение линей-ности графиков происходит на уровне магнитуд М=5.5-6.5. Более того, при исследовании редких сильных землетрясений возникают дополнительно осложняющие обстоятельства, когда угол измене-ния крутизны линии регрессии появляется два-жды.…”