There have been numerous observational studies of ionospheric

1
Introduction

• There have been numerous observational studies of
  ionospheric
• anomalies preceding strong earthquakes
• Two main hypotheses are put forward to explain
  how
• the earthquake preparation process could affect
  the ionosphere
• One hypothesis attributes this affection to some
  seismic origins low
• frequency oscillations of near-ground air
• The other one invokes as a primary source of the
  ionospheric
• variations perturbations of vertical electric
  field

2

• There are a number of observations of unusual
  perturbations
• of the vertical electrostatic field Ez at the
  earthss surface
• within a forthcoming earthquake epicentral zone
  under fair
• weather conditions.
• The perturbations amplitude ranged from tens to
  100 150
• V/m before moderate earthquakes and from hundreds
  up to
• 1000 V/m before strong earthquakes
• The physical mechanism of such perturbations of
  the vertical
• electric field Ez before earthquakes is far from
  being
• investigated

3
Z 0 km
Ez (V/m)
L T (h)
Fig. 1 The observed perturbation of the
atmospheric vertical electric field Ez near earth
surface prior to the Kamchatka earthquake of
K11.4 that occurred on September 24, 1997.
Adapted from Smirnov (2003).