Kefalonia Rocked By Two Aftershocks

Two Strong Aftershocks Rock Kefalonia

Mw 4.1, 9km south of Argostoli, Kefalonia, Greece, 14:22 UTC, 05/11/14; Mw 4.8, 10km south-south-west of Argostoli, Kefalonia, Greece, 07:41 UTC, 07/11/14.

 

The Mw 4.8 Argostoli Earthquake recorded on the Valsamata Seismograph, NOA NET. Two sizable aftershocks are visible (both in red on the right of the screenshot): Ml 3.6, 07:56 UTC & Ml 3.3, 10:54 UTC.

In the past two days two moderate aftershocks have struck the island of Kefalonia, Western Greece. The two earthquakes have occurred on a fault located near Kefalonia Airport in the south of the island.

Graphic created by J H Gurney showing the assumed strike-slip fault as suggested by the moment tensors of the 5th November Mw 4.1 & 7th November Mw 4.8 events - this graphic was created before the 7th November event was given a moment tensor solution by NOA.

An Mw 4.1 (Ml 4.2) earthquake struck on the 5th November at a depth of 12 kilometres. The moment tensor solution by NOA indicates a strike-slip faulting mechanism on an east-west striking fault, bisecting the Gulf of Argostoli at its mouth with the Ionian Sea.

The moment tensor solution information from NOA for the 5th November Mw 4.1 event. The beachball plot (top left) and map (bottom left) show a clear strike-slip earthquake at the mouth of the Gulf of Argostoli. Data on the right infers a nearly horizontal (dip = 86) fault plane with a east-west strike (strike = 270).  The rake (rake = -20) infers a minor normal faulting element to the quake. The earthquake is given a focal depth of 12 kilometres.

Earlier this morning an Mw 4.8 (Ml 4.7) earthquake struck at a depth of 18 kilometres. No moment tensor solution has yet been given by NOA, but judging by the many small earthquakes since the Mw 4.1 on the 5th November this earthquake will also be a strike-slip earthquake on the same fault.

The moment tensor solution information from NOA for the 7th November Mw 4.8 event. The beachball plot (top left) and map (bottom left) show a strike-slip earthquake with a minor reverse element (rake = 15) at the mouth of the Gulf of Argostoli. Data on the right infers a nearly steep (dip = 69) fault plane with a roughly east-west strike (strike = 263). The earthquake is a given a focal depth of 18 kilometres.

In January & February 2014 two magnitude 6 earthquakes struck the island, spawning numerous aftershocks and severely damaging the harbours at both Argostoli & Lixouri. Incredibly, despite the proximity to these major towns and the very shallow depth of the quakes, nobody was killed and between the two quakes only 23 people were injured.

Since the 3^rd February Mw 5.9 earthquake there has been a rapidly declining number of moderate aftershocks. These two earthquakes are of particular interest due to their location south of Argostoli, on the fringe of the immediate aftershock zone, and the fact these have occurred a full nine months after the mainshock. More shocks in the region of magnitude 4 are possible in the next few days and weeks.

This article was written on the 7th November 2014 by J H Gurney.