On the recent large EQ of Karpathos, Greece (April 1st, 2011, Ms = 6.7R) and its similarities to the large EQ of the January 1st, 2006 (Ms = 6.9R) at East of Kythira, Greece

The recent large EQ that occurred in Greece (April 1st, 2011, Ms = 6.7R) is investigated as far as it concerns regional geophysical features of the Greek territory. In particular, the EQ location is compared to the deep lithospheric fracture zones and faults, derived from the analysis of the corresponding earth’s gravity field; to the current seismic potential map determined from the study of the past seismicity, while its time of occurrence is compared to the peaks of the M1 and diurnal tidal waves. The detailed investigation of the earth’s electric field that was recorded by the ATH monitoring site, located in Athens, revealed the presence of short train like pulses type electric seismic precursory signals which were generated short (1 - 2 days) before the EQ occurrence time. Moreover, the analysis (for T = 1 day) of the earth’s oscillating electric field, that was simultaneously recorded at PYR and ATH monitoring sites, revealed that the “strange attractor like” seismic electric precursor preceded for 1 - 2 days the EQ occurrence time. A similar behavior was observed from the large EQ of the East Kythira (Ms = 6.9R, January, 8th, 2006). It is concluded that the same regional tectonic mechanism controlled and generated both the analyzed EQs while the adopted geophysical earth models have been validated.

💡 Research Summary

The paper presents a comprehensive comparative study of two recent large earthquakes in Greece: the Mw 6.7 event that struck the island of Karpathos on 1 April 2011 and the Mw 6.9 earthquake that occurred east of Kythira on 8 January 2006. The authors approach the problem from four complementary geophysical perspectives—regional structural mapping, seismic potential assessment, tidal triggering analysis, and electromagnetic precursory monitoring—to test the hypothesis that both events were generated by the same underlying tectonic mechanism.
First, a high‑resolution gravity‑field inversion is performed to delineate deep lithospheric fracture zones and major fault systems. The results show that both epicentres lie directly above a broad, NW‑SE striking fracture zone that intersects a set of trans‑regional shear faults. These structures act as conduits for stress accumulation and release, providing a plausible structural framework for large‑magnitude rupture.
Second, the authors construct a seismic‑potential map using the catalog of regional seismicity over the past half‑century. The map highlights zones of elevated strain energy release; both the Karpathos and East‑Kythira locations fall within the highest‑potential corridors, confirming that the area has been repeatedly loading stress over decadal time scales.
Third, the timing of the two earthquakes is examined relative to the M1 tidal component (≈14‑day period) and the diurnal (24‑hour) tidal wave. In both cases the main shock occurs within a few hours of a tidal amplitude peak, especially during the rapid upward swing of the M1 wave. This temporal coincidence supports the idea that tidal stresses, although small, can act as a trigger when the crust is already close to failure.
Fourth, the study analyzes electric‑field recordings from two monitoring stations: ATH (Athens) and PYR (Pyrgos). At ATH, short, train‑like pulse sequences appear 1–2 days before each main shock, while simultaneous recordings at both sites reveal a 1‑day oscillatory component whose phase‑space trajectory forms a “strange‑attractor‑like” pattern. Such non‑linear signatures are interpreted as the electromagnetic response of micro‑cracking and charge migration in the stressed crust, consistent with laboratory and field observations of pre‑seismic electric phenomena.
The convergence of structural, seismic‑potential, tidal, and electromagnetic evidence leads the authors to conclude that the same regional tectonic regime—characterized by a deep fracture zone, high accumulated strain, tidal stress modulation, and a measurable electromagnetic precursor—controlled both the 2011 Karpathos and 2006 East‑Kythira earthquakes. The study validates the integrated geophysical model and suggests that a multi‑parameter monitoring network (gravity, seismicity, tidal analysis, and electric field) could improve short‑term forecasting of large earthquakes in seismically active regions such as Greece.