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
(Instrument Analyseur Plasma), and ISL (Instrument Sonde de
Langmuir). ICE measures the three components of electric field
in a frequency range from DC up to 3.5 MHz, IMSC measures
the three components of magnetic field in ELF and VLF
frequency ranges, IDP measures ionospheric particles energy
(electron and proton), IAP measures temperature, density and
velocity of plasma ions, and ISL measures temperature and
density of plasma electrons.
1.2 Thermal anomaly precursor
Thermal anomaly is an unusual variation in surface temperature
that occurs around 1-13 days prior to the earthquake with
abrupt change in the temperature value of the order of 3-7? C or
more and disappears a few days after the event. Some remote
sensing satellites can measure the radiations coming from the
earth in thermal bands and provide useful information prior the
earthquakes. Due to their suitable temporal and spatial
resolutions, thermal infrared bands of Aqua-MODIS data have
been used.
2. APPLIED METHOD FOR ANOMALY DETECTION
AND ESTIMATE EARTHQUAKE PARAMETERS
In order to search for earthquake anomaly from precursor
variations a reasonable range for precursor regular variations
must be determined. The median and the inter-quartile range of
data are utilized to construct their upper and lower bound in
order to separate seismic anomalies from the background of
natural variations (Liu et al., 2004).
The upper and lower bound of the mentioned range can be
calculated using the following equations:
X44, 7 M + kX IQR (1)
Xoy "^ M -kxIQR Q)
—M
XQ, XX Xu = —k eDim ck (3)
IQR
where X. , Xhigh 0 P M.. IQR and Dx are the
parameter value, upper bound, lower bound, median value,
inter-quartile range and differential of x, respectively.
According to this, if the absolute value of Dx is greater than k,
(|Dx >k ), the behavior of the relevant parameter (x) is
regarded as anomalous. According to Eq. (3),
P = +100x (Dx m k)/ k indicates the percentage of
parameter change from the undisturbed state.
The results from our previous studies indicate that Dx value is
relatively proportional to the earthquake magnitude
(Akhoondzadeh, 2011). For instance, in large earthquakes with
a Dx value between 2 and 3, the magnitude value (My) is
estimated to be around between 7 and 8. The earthquake
magnitude estimation based on Dx value is shown in Table 1.
The radius of affected area can be estimated using the
Dobrovolsky formula: R = J ute , where R is the
radius of the earthquake preparation zone, and M is the
earthquake magnitude (Dobrovolsky et al., 1989).
DY value Earthquake
magnitude
D X<1 Mw«6
1<Dx< M ST
2< Dx <3 My 33
3< Dx 8<Mw
Table 1. Estimation of the earthquake magnitude.
Based on previous studies related to anomaly detection before
strong earthquakes mentioned in Table 2, the earthquake
anomalies may be observed 1 to 13 days prior to the
earthquake. If Dx value of a given day is greater than a
predefined threshold then based on the type of precursor, the
earthquake date is estimated according to the relation
HF 2.5X0 , (i.e. the fourth column) where 4/ and O are
the mean and standard deviation of values of the anomaly
observation day relative to the earthquake day (i.e. the third
column) (Akhoondzadeh, 2011).
In order to assess final earthquake parameters (which are date,
magnitude and radius of the affected area) for each case study,
using the median and inter-quartile range of earthquake
parameters obtained from different precursors, the approximate
bounds of final earthquake parameters are defined. For
instance, the date of impending earthquake is calculated based
on M + IQR , where M and IQR are respectively the
median and inter-quartile range of the predicted values of the
earthquake date for all precursors (Akhoondzadeh, 2011).
3. OBSERVATIONS AND CASE STUDIES
In order to clear up uncertainty to earthquake anomaly
detection, our study is based on a few types of precursors,
sensors and case studies. Using visual inspection in seismic
databases three earthquakes which happened in Samoa Islands,
Sichuan (China) and Boroujerd (Iran) have been incorporated
in this analysis. Table 3 indicates some characteristics of these
earthquakes.
3.1 Samoa Islands earthquake
In Samoa Islands, the largest earthquake so far, took place at
06:48:11 LT on 29 Sep 2009 with a Magnitude M,,=8.1. Table
4 illustrates the observed earthquake precursors concerning
Samoa earthquake.
As shown in Table 4 strong enhancement of TEC anomaly can
be seen during several time intervals (Akhoondzadeh et al.,
2010a).
Intern:
Prec
Ionos
Case Stud
Borujerd, Ir
Sichuan, Ch
Samoa Islar
Anomalous T
Sep 2009. Ba
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radius of affe
41.30 Km. TI
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