VLF sub-ionospheric signals and Earthquake
precursor signatures? Results from the studies
of some recent Earthquakes
Ajeet K Maurya, Rajesh Singh, B. Veenadhari
Indian Institute of Geomagnetism
New Panvel, Navi Mumbai – 410218, India
The Sharjah-Stanford AWESOME VLF Workshop Feb 22-24, 2010
Earthquakes: Facts and Nomenclature
EQMagnitude
Category
Number(/Year)
Energy Released
( 1015J/yr)
≥ 8.0
Great EQ
0-1
0-1,000
7-7.9
Major EQ
12
100
6-6.9
Strong EQ
110
30
5-5.9
Moderate EQ 1,400
5
4-4.9
Light EQ
13,500
1
3-3.9
Minor EQ
> 100,000
0.2
Source: Ionospheric Precursor of EQ, Springer
Earthquake prediction: A Challenge for Scientific
community
 People who live in a seismically active region of the
world would like to know when an earthquake will occur
 But Earthquake are notorious for striking suddenly.
 They cause death and devastation apparently without
warning
 Tens of thousand of lives and damage to the
structures and infrastructures could be saved, if early
warning are available

In last couple of decades scientific community is trying to
investigate problem of earthquake prediction by looking into:
(i) Are there other signals that rock produce when subjected to ever
increasing stress?
(ii) If such signals are produced at depth, can they be transmitted or
somehow carried from the seismogenic region to region of the
earth?
Lithosphere-atmosphere-Ionosphere Coupling – Types
Electromagnetic Coupling: Connected with the direct penetration
of DC electric field induced due to the appearance of Seismic-related
electric charges on the Earth’s surface. It can lead to substantial
modifications of ionospheric properties.
Chemical Coupling: Determined by the variation of the fair weather
electric field in the lower ionosphere due to the enhancement of
conductivity of lower atmospheric layer ionized by radon emanating
from Seismic faults.
Dynamic Coupling: Implies influence of atmospheric wave
processes originating near the Earth surface on the lower ionosphere.
Prospective pre-earthquake signals
 Local magnetic field variations over a wide range of timescales
 Enhanced infrared emissions from the epicentral region
 Change in the atmosphere near the ground and at altitudes up to ~ 1000 m
 Unusual animal behavior, etc
 Perturbations in the lower ionosphere above the epicentral region
 Anomalous behavior in Low/Ultra low electromagnetic emissions recorded
all around the globe
The scientific community has been deeply divided over these signals
and whether or not they are indeed pre-earthquake indicators
(Henderson et al., JGR, 1993; Rodger et al, Radio Sci., 1999 and others)
Ionospheric Precursors: For different ionospheric
layers
F-Layer: Critical frequency of F layer (foF2)
E-Layer: Critical frequency of Sporadic E-Layer (foEs)
D-Layer : Phase and Amplitude of ELF/VLF signals from
navigational transmitters
Out of these three types lot of work have been done by Japanese and
Russian group on D-region precursors studies.
( Pulinets et al 1991, Lipervosky et al 2000, Hayakawa 1996, Gokhberg et al., 1982;
Gufeld et al., 1992 )
Precursory Effects in D-layer : Use of VLF signals
 VLF waves are emerges as one of the most reliable and
important method for continuous D-region monitoring.
 The amplitude and phase distortion of the received VLF
Navigational transmitter signal were interpreted as influence of
the Earth-Ionosphere Waveguide where the VLF signals
propagates.
 This distortion is due to ionospheric lowering over the region
of the Earth-quake preparation.
 By the method of triangulation it is possible to determine the
position of future epicenter and form the distortion amplitude to
determine the EQ magnitude.
Earthquake Preparation Zone
 The area on the ground surface where precursory phenomenon
associated with the approaching Earthquake are observed. It is also called
the activation zone
 The radius of preparation zone is given as :
  10
0.43M
Km
Where ρ=radius of preparation zone, M= Earthquake magnitude
(Dobrovolsky et al 1979)
Primarily two methods of analysis is proposed using
sub-ionospheric VLF data to make out precursory
effects of ionospheric perturbations
 Terminator time method
 Night time fluctuation method
(1) Terminator Time Method
 Abnormal behavior occurs around the sunrise & sunset of local
times.
 Effective on E-W meridian plane propagation direction and Short
paths (~ 1000-2000 km)
 Evening Terminator is more indicative of Seismic influence
 Generally an increase in the evening terminator and decrease in
morning terminator time.
(Hayakawa et al., 1996; Molchanov and Hayakawa, 1998; Hayakawa 2007)
Kobe Earthquake (7.3 M) in 1995 (depth=20km)
 Reported significant shift in the terminator times before the
earthquake, inferring daytime felt by VLF signal is elongated for a
few days around the earthquake. – Hayakawa et al., 1996
Distance between receiver and transmitter is ~1000km
 Sift for Evening T-T is ~45 min.
(2) Nighttime fluctuation analysis
Use full for large distance (d>1000km)
 In this method VLF amplitude
corresponding Local night-time is
used.
 Estimate Diff : dA = A(t) - <A>
A(t) is the amplitude at time ‘t’
<A> is average over one month.
 Finally, integrate dA2 over the
night-time hours and have one data
value for one day.
(Shvets et al., 2004a, b; Roznoi et al., 2004; Maekawa at al., 2006)
Sumatra Earthquake – 26 December, 2004
M=9.0
depth=30km
– Hayakawa et al., 2007
– Hayakawa et al., 2007
Recent Earthquake
Observations
Facts about propagation paths
JJI and Allahabad:
Distance ~4800 km
Time difference: ~3:30 hrs
Direction form Allahabad ~ East
NWC and Allahabad:
Distance ~ 6300 km
Time difference: ~ 2:30 hrs
Direction form Allahabad ~ South-East
China Earthquake: Special Case
May 12, 2008 Wenchuan
Magnitude: 7.9 M
Epicenter location:
31.021°N 103.367°E
Depth: 19 km (12 mi)
Aftershocks: 149 to 284
major & over 42,719 total
TIME: 06:28:01.42 UT
Time diference~3.5hrs
Difficult to apply T-T method
T-T Method is not applicable
Adopted the Nighttime fluctuation analysis method
Adopted the Nighttime fluctuation analysis method
NWC Earthquake
Details of selected Earthquake
Date: 10-Aug-09,
Date: 30-Sep-09,
Location: Andaman Islands, India
Location: Southern Sumatra, Indonesia
Lat: 14.013N, 92.923 E
Lat: 0.725S, 99.856 E
Magnitude: 7.5, Depth: 33.1Km
Magnitude: 7.5, Depth: 81Km
Time: at epicenter, 19:55:39UT
Time: at epicenter, 10:16:09UT
Radius of Preparation Zone:1678.8Km Radius of Preparation Zone:1678.8Km
Date: 01-Oct-09,
Date: 02-Sep-09,
Location: Southern Sumatra, Indonesia
Location: Java, Indonesia
Lat: 2.508S, 101.484 E
Lat: 7.809S, 107.259 E
Magnitude: 6.6, Depth: 15Km
Magnitude: 7.0, Depth: 46.2Km
Time: at epicenter, 01:52:28UT
Time: at epicenter, 07:55:01UT
Radius of Preparation Zone: 688.68Km Radius of Preparation Zone: 1023.8Km
Methodology: T-T Method of analysis
10-Aug-EQ (Magnitude: 7.5, Depth: 33.1Km)
Change in Evening Terminator Time: ~11minute
Methodology: T-T Method of analysis
30-Sep & 1-Oct-EQ (Magnitude: 7.5, 6.6 Depth: 81Km, 15km)
Shift in Evening Terminator Time: ~20minute
Methodology: T-T Method of analysis
02-Sep-EQ (Magnitude: 7.0, Depth: 46.2Km)
Shift in Evening Terminator Time: ~22minute
Methodology: Night time Fluctuation Method of analysis
10-Aug-EQ (Magnitude: 7.5, Depth: 33.1Km)
Lowest
Methodology: Night time Fluctuation Method of analysis
30-Sep & 1-Oct-EQ (Magnitude: 7.5, 6.6 Depth: 81Km, 15km)
Lowest
Methodology: Night time Fluctuation Method of analysis
02-Sep-EQ (Magnitude: 7.0, Depth: 46.2Km)
Lowest
JJI-Earthquake
Date: 21-Sep-09
Date: 28-Aug-09,
Location: Bhutan,
Location: Northern Qinghai, China
Lat: 27.346N, Long:91.412E
Lat: 37.713N, 95.687 E
Magnitude: 6.1, Depth: 14Km
Magnitude: 6.2, Depth: 13Km
Time: at epicenter, 08:53:06 UT
Time: at epicenter, 01:52:06UT
Radius of Preparation Zone: 419.76 Km Radius of Preparation Zone: 463.45 Km
Both method of analysis have been applied:
T-T Method of Analysis
No Change in Terminator Time
Night time Fluctuation Analysis
Lowest
It shows the lowest value of
fluctuation amplitude on the
day of EQ compared the days
around the EQ days.
Lowest
It shows the lowest value of
fluctuation amplitude two days
before the EQ day.
Summary
 So, we clearly see the increase in the VLF
amplitude fluctuation for 12 May, 2008 China
Earthquake
 This is not true for all the Earthquakes
 In case of Andaman and Indonesian we see lowest
values of fluctuation on EQ day - with increase before
and after EQ
 Clear shift in Evening Terminator time ~ 10 – 25 min
for Andaman and Indonesian EQ is seen
No Uniform Pattern is Observed
 Subject of Seismic-Ionospheric perturbations caused by
Earthquakes needs more attention and study
Thank you for your
kind attention