Synopses of Master Papers

Bulletin of IISEE, 47, 1-6, 2013

CRUSTAL DEFORMATION OF THE MID NIIGATAREGION DERIVED FROM GPS MEASUREMENTSASSOCIATED WITH THE 2004 CHUETSU, THE 2007
CHUETSU-OKI, AND THE 2011 M W 9.0 TOHOKU-OKI
EARTHQUAKES
Rafig Safarov ∗MEE11601

Supervisor:

Takeshi SAGIYA ∗∗ABSTRACT
The published F3 final daily coordinate solutions from GEONET (GPS Earth Observation Network)
were analyzed to investigate the crustal deformation of the Mid Niigata (Chuetsu) region associatedwith the 2004 M6.8 Chuetsu, the 2007 M6.8 Chuetsu-oki, and the 2011 M w 9.0 Tohoku-oki
earthquakes. This kind of study is important to understand the effect of large earthquakes onsurrounding faults, to have information about how the conditions of fault failure have been changed
and eventually to progress the long-term forecast of crustal processes. High strain rates were estimatedafter the 2011 Tohoku-oki earthquake in the Mid Niigata region as well as in eastern Japan. We
inferred that the deformation field of the Mid Niigata region is generally controlled by the west-east
contraction due to the interactions between the Amurian and the Pacific plates. We found the strain
redistribution in the period between the 2004 and the 2007 events. Since between the 2004 and the2007 earthquakes significant seismic event was not observed in the Mid Niigata region, we interpreted
this strain redistribution as a slow slip event with representation of a single, rectangular fault.
Keywords: Coseismic step, Displacement rate, Dilatation, Shear strain

1. INTRODUCTION
Previous crustal deformation studies in Japan based on GPS measurements have been done by several
researchers (Sagiya et al., 2000; Iinuma et al., 2005; Ohta et al., 2008). In the research which has been
done by Sagiya et al. (2000), it was pointed that a strain concentration zone with considerable width
extends from Niigata to Kobe. This deformation belt is named Niigata-Kobe Tectonic Zone (NKTZ).
Here the crust is contracting in the NW-SE direction and a similar contraction is likely to occur in theChuetsu region which is located in the northern part of the NKTZ (Iinuma et al., 2005). Normal faults
which were formed at the stage of extensional stress regime have been subsequently activated asreverse faults during shortening in the eastern margin of the Japan Sea in the past 3.5 Ma (Okamura etal., 1995; Ikeda et al., 2002; Sato et al., 2004). The 1964 M 7.5 Niigata earthquake, the 2004 M 6.8Mid-Niigata Prefecture (Chuetsu) and the 2007 M 6.8 Niigata-ken Chuetsu-oki earthquakes ruptured
such reverse faults. The dense GPS network in Japan enables us to calculate co-seismic strain andstress changes from observed data.

∗

Geology Institute of Azerbaijan National Academy of Sciences, Baku , Azerbaijan.
Professor, PhD, Disaster Mitigation Research Center, Nagoya University, Japan.

∗∗2. THEORY AND METHODOLOGY

2.1 Displacement Rate Analysis
We estimated the displacement rate of GPS stations based on daily coordinate solutions (F3). In orderto do this we fitted the following function to daily time series data of the i-th coordinate component ofthe n-th station.
𝑚𝑖𝑥𝑛𝑖 (𝑡) = 𝑎𝑛𝑖 + 𝑏𝑛𝑖 𝑡 + 𝑐𝑛𝑖 𝑠𝑖𝑛(2𝜋𝑡) + 𝑑𝑛𝑖 𝑐𝑜𝑠(2𝜋𝑡) + � 𝑒𝑛,𝑘𝐻�𝑡 − 𝑡𝑛𝑘 �
𝑘=1(1)

Here, the first two terms on the right side correspond to a linear trend, the next two terms to asinusoidal annual variation, and the last term to coseismic steps. Coseismic steps are described as a𝑖𝑖𝑘
sum of Heaviside functions, ∑𝑚𝑘=1 𝑒𝑛,𝑘 𝐻�𝑡 − 𝑡𝑛 � where 𝑒𝑛,𝑘 is a magnitude of the k-th step which
occurred at 𝑡𝑛𝑘 . The coefficient 𝑏𝑛𝑖 is an estimate of displacement rate. We applied this expression to
all three components separately, and estimated displacement rate components for all stations bysolving least-squares problems (Sagiya et al., 2000).

2.2 Strain Rate Analysis
Using the method by Shen et al. (1996) we have calculated strain rates as a continuous function within
the entire network. It is assumed that the strain rate field is uniform at each location. We applied theleast squares inversion method to velocity solutions of all stations and their covariances to solve forsix parameters: horizontal velocity components, rotation rate, and strain rate components. Thenmaximum shear strain rate and the dilatation rate were derived from the three strain rate components.
The strain rate modeling algorithm can be written in the following form:

1 0𝑈� �=�𝑉0 1∆𝑥𝑖 ∆𝑦𝑖0 ∆𝑥𝑖

0∆𝑦𝑖𝑢⎡ 𝑣 ⎤𝜀𝑥𝑖∆𝑦𝑖 ⎢𝑒̇𝑥𝑥 ⎥� ⎢𝑒̇ ⎥ + � 𝑖 �−∆𝑥𝑖 ⎢ 𝑥𝑦 ⎥𝜀𝑦⎢𝑒̇𝑦𝑦 ⎥⎣𝜔⎦(2)where (U, V ) – displacement rate observed at a station which is located at point X=(X, Y). (u, v ) –horizontal displacement rate components, 𝑒̇𝑥𝑥 , 𝑒̇𝑥𝑦 , 𝑒̇𝑦𝑦 – strain rate components and ω - rotation rate
are to be calculated at a particular point 𝒙𝑖 = (𝑥𝑖 , 𝑦𝑖 ). ∆𝑥𝑖 =X – 𝑥𝑖 , and ∆yi =Y - yi and 𝑒̇𝑥𝑦 =1(𝜕𝑢/𝜕𝑦) + (𝜕𝑣/𝜕𝑥). (𝜀𝑥𝑖 , 𝜀𝑦𝑖 ) are the observational errors and they are weighted depending on the2

distance between the observation point X and the calculation point 𝑥𝑖 in the following formula.
𝑖𝑖𝜀𝑥,𝑦= 𝜎𝑥,𝑦exp(Δ𝑅𝑖2 /2𝐷2 )(3)𝑖Here, 𝜎𝑥,(𝑦)is an original observational error of the x (or y) component of thedisplacement rate, 𝛥𝑅𝑖 = |𝑋 − 𝑥𝑖 | , and D is a parameter which controls weight among theobservations and is called the Distance Decaying Constant (DDC). It depends on tectonic deformation
features and density of observational points. Then we used the following formulas to calculate
dilatation rate Δ and shear strain rate Σ at each point.

Δ = 𝑒̇ 𝑥𝑥 + 𝑒̇ 𝑦𝑦Σ = �𝑒̇𝑥2𝑦 + (𝑒̇ 𝑥𝑥 − 𝑒̇ 𝑦𝑦 )2 /4(4)3. RESULTS AND DISCUSSION
3.1 Displacement rate results
We calculated displacement rate distributions using daily coordinates from 2002 to 2006, namely two
years before and after the 2004 M 6.8 Chuetsu and from 2005 to 2009 for the 2007 M 6.8 Chuetsu-oki
earthquakes which occurred in our study area. In addition, in order to see the impact of the big seismic
event such as the 2011 M W 9.0 Tohoku-oki earthquake on a deformation pattern of our target area wealso have calculated displacement rates from 2009 to 2012, two years before and one year after thisearthquake.
3.2 Strain rate results
To make our results independent from reference frame and to be able to discuss deformation field
related to local crustal processes we performed strain rate analyses. In our calculations we applied 20
km as a value of Distance Decaying Constant.
From comparison of all dilatational and maximum shear strain results for all time-periods
except after the great 2011 Tohoku-oki earthquake we can conclude that they represent almost thesame pattern. Previously, found by Sagiya et al. (2000) continuously high (over 0.1 micro-strain/year)
strain rate zone which starts from around the Japan Sea coast near Niigata and continues to Kobe
(Niigata-Kobe Tectonic Zone) can be clearly seen from our results. In addition, low strain rates foundat the Kanto area which is consistent with results of previous studies (Sagiya et al., 2000). Anotherhigh positive dilatational rate (over 0.2 micro-strain/year) is estimated at Izu Peninsula. This can beinterpreted as a result of volcanic activity due to the plate interaction near the northern end of thePhilippine Sea plate. After the great 2011 Tohoku-oki earthquake the deformation pattern of Japansignificantly changed (Figure 1b). Compressional deformation pattern changed to extensional almost
all over the Japanese islands (Figure 1). Although principal strain axes before this event show thewest-east contraction, whereas they changed to the west-east extension after the event.
The calculated dilatation and strain rate distributions for the 2011 Tohoku-oki earthquake
are slightly different from each other (Figure 1b and Figure 2b). However, both plots show high strain
rates over 0.7 micro-strain/year from Mid Niigata to northernmost Aomori. As we mentioned above
before the 2011 Tohoku-oki earthquake high strain rates over 0.1 micro-strain/year can be seen at
Niigata-Kobe Tectonic Zone except at the Izu Peninsula (Figure 2a).

a)b)Figure1.
Dilatation
rate
distributions and corresponding
principal strain axes two years
before (a) and after (b) the 2011
M W 9.0 Tohoku-oki earthquake.

However, after this event strain
rates 2-4 micro-strain/year stillhigh in eastern Japan (Figure 2b).
Before the 2011 Tohoku-oki
earthquake the strain rates at theChuetsu region were between
0.1-0.2 micro-strain/year (Figure2a). After the 2011 event the strain rate at the Chuetsu region increased to 0.7-0.9 micro-strain/year

(Figure 2b). This big difference of strain rates shows that it will require a long time to go back to theprevious deformation pattern of Japan.

a)b)Figure 2. Strain rate distributions
and corresponding principal strain
axes two years before (a) and after(b) the 2011 M W 9.0 Tohoku-oki
earthquake.

From the above discussions weinfer that the deformation field of
our target area – Mid Niigata regionis generally controlled by thewest-east contraction due to theinteractions between the Amurian
and the Pacific plates. However,this kind of discussions could not represent local crustal processes occurring in such a small area as
Chuetsu region. Thus, in order to understand crustal processes which have been the cause of the twonotable earthquakes in this area we performed strain analyses with high resolution.

a)b)

Figure3.
Dilatation
rate
distributions and corresponding
principal strain axes two years
before (a) and after (b) the 2004 M
6.8 Chuetsu earthquake.

Before the 2004 event we observed
over
0.2
micro-strain/year
contraction near the source regionboth in dilatational and maximum
shear strain rate plots (Figure 3a;
Figure 5a). However, during two
years after this event high strain
again has been accumulated at the source region of the 2004 event (Figure 3b; Figure 5b). Two years
before the 2007 M 6.8 Chuetsu-oki earthquake, there was high contraction over 0.3 micro-strain/year
at the source region of this event which is also reasonable (Figure 4a; Figure 6a).

a)b)

Figure4.
Dilatation
rate
distributions and corresponding
principal strain axes two years
before (a) and after (b) the 2007 M
6.8 Chuetsu-oki earthquake.

During two years after the 2007
event there was no significant strain
accumulation near the source region
and thus, we found the field has
totally changed compared with theprevious time-periods (Figure 4b;Figure 6b). The important point tonote here is the period between the 2004 and the 2007 events. After the 2004 event we observed highstrain rates at the source region of this event (Figure 5b). However, for the time-period of 2005-2007
we found that this pattern changed and a high strain zone shifted to the source region of 2007 event.

a)Figure 5. Strain rate distributions
and corresponding principal strain
axes two years before (a) and after(b) the 2004 M 6.8 Chuetsuearthquake.

b)

The question is what happened
during this period between thesource regions of these two events.
Since we did not observe asignificant seismic activity between
these two events, in order to answer
to this important question we havecalculated displacement rate distribution for this time-period and tried to interpret this as a slow slip
event with representation of a fault (Figure 7).

a)Figure 6. Strain rate distributions
and corresponding principal strain
axes two years before (a) and after(b) the 2007 M=6.8 Chuetsu-okiearthquake.

b)

Theoretical crustal deformation
wascalculated
basedonhorizontal component data byusing a simple, rectangular fault
model in an elastic half space(Okada, 1985). We used 0.25 as avalue of Passion’s ratio in ourcalculation. Our fault has a west dipping plane and lies about 8 km south-west from the source regionof the 2004 Chuetsu earthquake. Assuming a rigidity of 30 GPa, we obtained moment magnitude M w= 6.1 and the total amount of the slow slip for the period between events is estimated at 0.35 m. The
estimated fault parameters are shown in Table 1.
Figure 7. Observed (black arrows) and calculated (red arrows)
displacement rate distribution for the interseismic period between
the 2004 M 6.8 Chuetsu and the 2007 M 6.8 Chuetsu-oki
earthquakes. Blue line shows the surface trace of the simplified

fault model and the green line represents the 9-km depth
position of the fault for a 32 degree dip angle.

Table 1. Estimated fault parameters of proposed slow-slip event for
the interseismic period between the 2004 M 6.8 Chuetsu and the2007 M 6.8 Chuetsu-oki earthquakes.
Latitude(deg)37.29

Longitude(deg)138.778

Depth(km)9.0Strike(deg)190

Dip(deg)
32Rake(deg)
79

L(km)
14.50

W(km)
12.0

Slip(m/year)
0.13

Mw
6.1

4. CONCLUSIONS
We found significant strain rate changes in eastern Japan due to the 2011 Tohoku-oki earthquake.
Strain rates in the Chuetsu region before and after the 2011 Tohoku-oki earthquake were also
calculated. We inferred that the deformation field of our target area – Mid Niigata region is generally
controlled by the west-east contraction due to the interactions between the Amurian and the Pacificplates. We found strain redistribution in the period between the 2004 and the 2007 events. We tried tointerpret this strain pattern change by a slow slip event with representation of a fault. We estimated thefault area to be 14.5 × 12 km2. The strike, the dip and the rake of the source were estimated at 190°,32°, 79° respectively. The depth of the upper edge of the fault was found as 9 km. Assuming a rigidityof 30 GPa, we obtained moment magnitude M w = 6.1 and the total amount of the slow slip for theperiod between events is estimated at 0.35 m.

5. RECOMMENDATION
Since 1998 Geology Institute of Azerbaijan National Academy of Sciences has started the monitoringof crustal processes and currently Azerbaijan GPS network consists of 3 continuous GPS stations and35 campaign survey points, which are not enough for the discussions of the deformation field.
Therefore, it is needed to increase number of continuous GPS stations in order to be able to monitor
time-dependent deformation all over the region and to get better resolution of deformation field.

ACKNOWLEDGEMENT
I would like to express my heartiest gratitude to my advisor Dr. B. Shibazaki and Dr. Yokoi for theirvery useful advices and suggestions during my individual study. Also, I express my sincere gratitude
to the GPS group of GSI for their effort in keeping operation of GEONET and publishing all the datafor public.

REFERENCES
Iinuma, T., et al., Geophys. J. Int.,160(2), 417–434, 2005.
Ikeda, Y., Active Fault Research, 22, 67-70, 2002 (in Japanese with English abstract).
Ohta, Y., et al., Earth Planets Space, 60, 1081-1086, 2008.
Okada, Y., Bulletin of the Seismological Society of America, v. 75, no. 4, p. 1135-1154, 1985.
Okamura, Y., Watanabe, M., Morijiri, R., and Satoh, M., Island Arc, 4, 166-181, 1995.
Sagiya, T., Miyazaki, S. and Tada, T., PAGEOPH, 157, 2303–2322, 2000.
Sato, H., et al., Tectonophysics, 388, 47-58, 2004.
Shen, Z., Jackson, D. D., and Ge, B. X., J. Geophys. Res. 101, 27,957-27,980, 1996.