ELF/VLF waves as Earthquake precursor– A case study

(May 12, 2008 Wenchuan, China earthquake)

Rajesh Singh, A.K. Maurya, B. Veenadhari, P. Pant1, A.K. Singh2

Indian Institute of GeomagnetismNew Panvel, Navi Mumbai - 410218 India

1ARIES, Manora Peak, Nainital – 263129, India2Physics Department, B.H.U. , Varanasi – 221005 India

VTX

NWC

JJI3SA

ICVHWU

FTA2

DHQGBR

Allahabad

Nainital

VNS

May 12, 2008 Wenchuan China earthquake

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

Predicting an earthquake is and has always been a challenge for Scientific Community

Seismologists Quote:

‘Earthquakes cannot be predicted’

- Geller, R.J., Jackson, D.D., Kagan, Y.Y., Mulargia, F., Science, 275, 1616, 1997

- Main, I., Nature, 385, 19, 1997

This statement is true if the only tools for prediction are those of Siesmology and Geodesy: Earthquakes can indeed not be predicted

Because what ever the probability models for prediction available in seismology are based on past seismograph data and geological records

- Friedemann, T.F. Current Science, 94, 311, 2008

The data that goes into these models are retrospective: The knowledge acquired over the past events is used to forecast future events – Statistical Analysis

So, even the most elaborate models is inadequate because it is not based on information that might become available in real time about a specific earthquake that looms ahead

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?

Prospective pre-earthquake signals

Anomalous behavior in Low/Ultra low electromagnetic emissions recorded all around the globe

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 behaviour, etc

Perturbations in the lower ionosphere above the epicentral region

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)

VLF/LF radio sounding Search for Seismo-ionospheric perturbations:

Previous Works

First attempt was done by Russian workers (Gokhberg et al., 1982; Gufeld et al., 1992). They studied long VLF path form Reunion Omega transmitter to Omsk and Moscow, looking for any earthquake effect in the Caucasia region – Found anomaly for Spitak earthquake

Kobe Earthquake (7.3 M) in 1995

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

Later a much more extensive study by Molchanov and

Hayakawa, 1998 based on much more events during 13

years for same propagation path Tushima to Inubo came to

following conclusions:

(i) For shallow earthquakes (depth < 30 km), terminator time

anomaly was found similar to Kobe earthquake

(ii) When the depth is in medium range of 30-100 km, different

type of terminator time anomalies were found

(iii) Deep (> 100 km) earthquakes did not showed any anomaly

– Hayakawa et al., 2007

Sumatra Earthquake – 26 December, 2004

– Hayakawa et al., 2007

May 12, 2008 Wenchuan, China earthquake (19th deadliest earthquake of all time)

Depth: 19 kilometres (12 mi)

Epicenter location: 31.021°N 103.367°E

Aftershocks: 149 to 284 major & over 42,719 total

Casualties: ~ 69,000 dead~ 18,000 missing ~ 375,000 injured

Magnitude: 7.9 M

TIME: 06:28:01.42 UT

Tested all the proposed method of analysis

Primarily two methods of analysis is proposed using sub-ionospheric VLF data to make out precursory effects of ionospheric perturbations

(1) Terminator Time Method

Effective on E-W meridian plane propagation direction and Short paths (~ 1000-2000 km)

(Hayakawa et al., 1996; Molchanov and Hayakawa, 1998; Hayakawa 2007)

(2) Nighttime fluctuation analysis

0 2 4 6 8 10 12 14 16 18 20 22 24-4

-2

0

2

4

6

8

IST(Hours)

Am

pli

tud

e(a

.u.)

dA=A(t)-<A>

<A>

A(t)

<A>

A(t)

dA=A(t) - <A>

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

0 2 4 6 8 10 12 14 16 18 20 22 24

JJI-Allahabad: Daily Amplitude Variation

Time in LT

20-April

29-April

11-May

EQ-12-May

16-May

0 2 4 6 8 10 12 14 16 18 20 22 24

JJI-Nainital: Daily Amplitude Variation

Time in LT

21-April

11-May

EQ-12-May

20-May

0 2 4 6 8 10 12 14 16 18 20 22 24

JJI-Varanasi: Daily Amplitude Variation

Time in LT

20-April

11-May

EQ-12-May

20-May

Daily Amplitude Variations at NAT, ALD and VNS

0 2 4 6 8 10 12 14 16 18 20 22 24

JJI-Allahabad: Daily Amplitude Variation

Time in LT

20-April

29-April

11-May

EQ-12-May

16-May

Terminator -Time not visibleTerminator -Time not visibleT-T method not

applicable

~5500 km

Time Difference ~ 3.5 hrsDifficult to apply T-T method of analysis

12 14 16 18 20 22 24

JJI-VNS: Daily Night Time Amlitude Variation

Time in UT

20-April

11-May

EQ-12-May

16-May

12 14 16 18 20 22 24

JJI-NAT: Daily Night Time Amlitude Variation

Time in UT

20-April

11-May

EQ-12-May

20-May

12 14 16 18 20 22 24

JJI-VNS: Daily Night Time Amlitude Variation

Time in UT

20-April

11-May

EQ-12-May

20-May

Adopted the Nighttime fluctuation analysis method

0

200

400

600

800

1000

1200 JJI-ALD: Night Fluctuations

Flu

ctu

atio

n (

a.u

.)

20-April

EQ-12-M

ay

16-May

0

2000

4000

6000

8000

10000 JJI-NAT: Night Fluctuations

Flu

ctu

atio

n (

a.u

.)

20-April

EQ-12-May

20-May

0

1000

2000

3000

4000

5000

6000

7000

8000

9000 JJI-VNS: Night Fluctuations

Flu

ctu

atio

n (

a.u

.)

19-April

EQ-12-May

20-May

Kp < 4

So ionospheric perturbation due to solar activity can be ruled out

DEMETER Q-look ELF Spectrum

06 May 2008Orbit: 20545_0

07 May 2008Orbit: 20560_0

08 May 2008Orbit: 20575_0

09 May 2008Orbit: 20589_0

10 May 2008Orbit: 20604_0

11 May 2008Orbit: 20619_0

E-quake12 May 2008

Orbit: 20633_0

13 May 2008Orbit: 20648_0

Orbit Time ~ 4-5 UTEQ TIME: 06:28:01.42 UT

Thank you for kind attention !

These are initial observations - NOT conclusions on EQ precursors