XIX-B8, 2012
] 8. The earthquake
: shown in Table 1.
estimated using the
696 ;
, Where R is the
zone, and M is the
, 1989).
ke
le
ke magnitude.
naly detection before
> 2, the earthquake
days prior to the
iy is greater than a
ype of precursor, the
ng to the relation
where L4 and O are
lues of the anomaly
«e day (i.e. the third
ters (which are date,
) for each case study,
ange of earthquake
sors, the approximate
s are defined.’ For
ce is calculated based
are respectively the
edicted values of the
idzadeh, 2011).
E STUDIES
earthquake anomaly
types of precursors,
nspection in seismic
ied in Samoa Islands,
ve been incorporated
1aracteristics of these
so far, took place at
nitude M,z8.1. Table
recursors concerning
of TEC anomaly can
\khoondzadeh et al.,
International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Volume XXXIX-B8, 2012
XXII ISPRS Congress, 25 August — 01 September 2012, Melbourne, Australia
Anomaly observation day Estimated earthquake day
Precursor Reference relative to the earthquake relative to the observation day
day
Ionospheric Zhao et al., 2008 5 15
Liu et al., 2004 4
Pulinets et al., 2003 5
Akhoondzadeh et al., 2010a, 2010b 11
Akhoondzadeh and Saradjian, 2010 8
Thermal Ouzounov and Freund, 2004 6 16
Saraf and Choudhury, 2005a 13
Choudhury et al., 2006 7
Pulinets et al., 2006 7
Saraf and Choudhury, 2005b 8
Table 2. Estimation of the earthquake date.
Case Study Date Time (UTC) Longitude Latitude Magnitude (My) Focal depth (km)
Borujerd, Iran 2006/03/31 01:17:01 48.78 N 33.50 E 6.1 7
Sichuan, China 2008/05/12 06:28:01.57 103.32 N 310F 7.9 19
Samoa Islands 2009/09/29 17:48:10.99 172.10 W 15.49 S 8.1 18
Table 3. List of the earthquakes selected in this study (reported by http://earthquake.usgs. gov/)
Anomalous TEC variations of the order of 2.55 began on 24
Sep 2009. Based on proposed method, this anomaly indicates
that an earthquake with a magnitude between 7 and 8 would
have been happened between 25 Sep and 9 Oct 2009 and the
radius of affected area would have been between 15.92 and
41.30 Km. The TEC anomaly on 28 Sep 2009 was expanded
and amplified with a maximum value reaching 3.73 at 03:00
LT. For Dx=3.73 the magnitude of impending earthquake,
which would have been occurred between 29 Sep and 13 Oct
2009, is estimated to be greater than M,=8.0. Therefore, the
radius of affected area is estimated to have been greater than
41.30 km.
Table 4 also illustrates variations of different parameters
extracted from DEMETER experiments data over Samoa
region. An increase in total ion density is clearly observed at
~10:30 LT on 25 Sep 2009. Variations of total ion density
clearly exceed the upper bound of the order of 67%
(Akhoondzadeh et al., 2010a). This precursor indicates that an
earthquake with a magnitude greater than M,=8.0 would have
been occurred between 26 Sep and 10 Oct 2009. Similar to this,
another unusual behavior is seen in electron density variations,
when it reaches a maximum value, at ~10:30 LT, and exceeds
the upper bound of the order of 67% on 25 Sep 2009. Because
of the inverse relation between electron density and electron
temperature, observed anomaly in electron density can be
acknowledged by the electron temperature variations. Table 4
indicates that electron temperature has reached to its minimum
value (Dx=-1.82) at ~10:30 LT, on 25 Sep 2009. This anomaly
indicates that an earthquake with a magnitude between 6 and 7
would have been happened between 26 Sep and 10 Oct 2009.
Irregularities of electron density also occurred at ~22:30 LT,
18, 21, 24 and 26 Sep 2009 that among them, the maximum
irregularity intensity (i.e. 60.5%) was observed on 24 Sep 2009.
According to this anomaly an earthquake with a magnitude
between 7 and 8 would have been happened between 25 Sep
and 9 Oct 2009 and the radius of affected area to have been
between 15.92 and 41.30 km.
Table 4 represents the intense appearance of the NPM
transmitter waves in the VLF electric spectrogram on 21 Sep
2009. This strong electromagnetic enhancement of the VLF
transmitter wave is due to the broadening of the spectral
component at the transmitter frequency. This broadening is
enhanced when the VLF wave crosses ionospheric irregularities
(Bell and Ngo, 1988). This sharp appearance is also seen in the
VLF magnetic spectrogram at the same time (Akhoondzadeh et
al., 2010b). These earthquake precursors extracted using ICE
and IMSC experiments indicate that an earthquake with a
magnitude greater than M,z7, would have been happened
between 22 Sep and 6 Oct 2009. Table 4 also represents the
attenuation of the NPM transmitter signals when they crossed
the disturbed ionosphere on 24 Sep 2009. This fading of the
signal can be associated to an increase of the ionospheric
density because during the ionospheric propagation the signal
attenuation is directly proportional to the plasma density
(Cannon and Bradley, 2003). The analysis of HF electric
spectrogram shows the intense appearance of harmonic
emissions above NPM transmitter on 28 Sep 2009
(Akhoondzadeh et al., 2010b).
The final earthquake parameters including the date, magnitude
and radius of affected area are estimated using the earthquake
parameters deduced from different precursors. The bounds of
the final impending earthquake parameters are calculated using
the median and inter-quartile range of earthquake parameters
estimated using different precursors. In this case study, it is
predicted that an earthquake would have been happened with a
magnitude between 7 and 8, on a date between 29 September
and 6 Oct 2009, and in an affected area of radius between 15.92
and 41.30 Km. The Samoa earthquake actually happened on 29
September 2009 with a magnitude M,=8.1.
