Satellite based observations
The research was based on analysis of the data obtained from micro-satellites such as French DEMETER and Russian COSMOS-900, together with publicly available data from the Cluster (ESA) and THEMIS (NASA) missions. The main objective of the DEMETER satellite was to search for and characterise ionospheric perturbations that may be associated with seismic activity. Presently, DEMETER has been the only satellite which has the capability of surveying the Earth's electromagnetic environment in the ionosphere on a global scale to search for seismic related phenomena. The high-quality database created during the mission (which contains measurements from October 2004 to December 2010) allows us to perform the statistical analysis which is necessary to ascertain the link between the recorded perturbations and seismic activity.
In addition to DEMETER, data from the plasma density analyser onboard COSMOS-900 was used to provide further observations of the plasma environment.
The occurrence of plasma waves has also been investigated. This study was based on data obtained from the Cluster and THEMIS missions, which provide measurements of the electric and magnetic field fluctuations in the ULF frequency range.
In addition to satellite observations, the propagation characteristics of signals from powerful radio transmitters deployed in Europe, United States, Asia, and Australia have been analysed using data from a specialised VLF/LF (10-50kHz) network of receiving stations distributed in Russia (Petropavlovsk-Kamchatsky, Yuzhno-Sakhalinsk and Moscow), Europe and Japan. This network enabled the search for electromagnetic earthquake precursors in highly seismo-active regions such as the Far East (Sakhalin Island, Kurile Islands and Japan) and Southern Europe.
Seismic zones to be studied
Sakhalin Island and the Kurile Islands
Sakhalin Island and the Kurile Islands lie inside the Pacific seismic zone which is characterised by extremely strong seismic activity. The hypocenters of earthquakes that occur in the region of the Kurile Islands or in the Ohotskoe Sea are mainly localised in a seismofocal zone nearly 70km wide that runs under the continent at depths of up to 650km. This zone crops up near the deep Kurile trench, about 60-70km east of the Kuriles. Seismic activity reaches its maximal value in this region in which more than half of the earthquakes occur at depths of 30-50km. Usually one earthquake with magnitude M>8 and around 10 other events with M>7 are recorded each decade.
The hypocenters of strong earthquakes in the vicinity of Sakhalin Island are associated with the West-Sakhalin, Central Sakhalin, and East-Sakhalin faults or with their feathering faults. The seismic activity of the Sakhalin crust is more moderate, typically with one earthquake with M>6 and around 10 events with M>5 recorded on Sakhalin territory each decade.
The most destructive earthquakes to have occurred in this region during last 18 years are as follows:
- Shikotan (1994, Mw=8.3, h=40 km)
- Iturup (1995, Mw=7.9, h=50 km)
- Neftegorsk (1995, Ms=7.2, h=18 km)
- Uglegorsk (2000, Ms=7.2, h=18 km
- Nevelsk (2007, Mw=6.2, h=10 km)
The seismic activity of Southern Europe is much weaker. Earthquakes with M>6.5 occur very seldom. However, due to their shallow depth (hypocenters about 10km), their effects are much more widely felt. Europe has a rather high population density and so these earthquakes may result in extensive damage with many victims.