Geodesy and Geodynamics 2014,5 ( 4) :16-24

http ://www.jgg09.com

Doi: 10.3724/SP .].1246.2014.04016

Analysis of the Badong MsS. 1 earthquake source characteristics

Wu Haiho1' 2 , Chen Junhua1' 2 , Shen Xuelin1'2 , Zhang Lifen1'2 , Zhao Lingyun1'2and Zhang Ke' 1 Key laboratory of Earthquake Geocksy, [,..titute of Seismology, Chi= Earthquake Administration, Wuhan 430071 , Chino 2 Earthquake Administration of Huhei PrmJince, Wuhan 430071, Chino 3 Earthquake Adminutration of Shiyan CU,., Shiyan 442000, Chi=

Abstract: The mainshock location of the Badong Ms5. 1 earthquake is determined using four location methods :

the simplex method, HYP2000, hyposat, and locSAT; the 350 aftershocks over 3 months are relocated using

the double difference location method. The results indicate that aftershocks are distributed as bands along the

NEE direction and that the aftershocks 1 month after the mainshock , which are mainly distributed in the west

of the mainshock and near the Gaoqiao fault, are shallow earthquakes within 5 km ; the depth of each after-

shock after one month is deeper, and two distinct fault planes , for which the geological occurrence is similar to

the Gaoqiao and Zhoujiashan-Niukou fault, are shaped. The frequency-spectrnm analysis of the recorded wave-

form in 12 seismic events indicates that the comer frequency of the mainshock is significantly lower than that of

its aftershock and is also lower than a tectonic earthquake of the same magnitude. We considered that this re-

sult is related to the constraint of the parameter calibration relationship in the focal spectrum and the lithology

change due to water erosion. Combined with the focal mechanism and geological tectonic setting, we conclude

that the occurrence of the earthquake is related to the activity of the Daping and Gaoqiao fault and is a reser-

voir-induced tectonic seismicity.

Key words: precise location of the mainshock ; double difference location ; deep profile ; comer frequency

1 Introduction

The epicenter of the Badong Ms5. 1 earthquake in 2013

was located less 5 km to the north shore of the Yangtze

Three Gorges Reservoir. As of March 15, 2014, there

have been more than 800 aftershocks. It is the largest

earthquake since the Three Gorges reservoir was initial-

ly impounded in 2003 and was also a typical reservoir-

induced earthquake since the Xinfengjiang Ms6. 1

earthquake in 1962[t,zJ.

The epicenter nf the earthquake was near the Gao-

qiao fault and the Daping fault of Badong. The under-

Roceived, 2014-04-23; Aooepted, 2014-08-25

Corresponding authm: Wu Haibo, E-mail: wuhaiho7777@ 163.com.

This work is supported by the Spark Program of Earthquake Sciences

(XH14035YSX).

ground rocks in the region are mainly limestone and

gypsum rocks , and Karst caves are widely distributed.

The epicenter also lies in the water permeability zone of

the Three Gorges reservoir, and so the seismogenic

mechanism and cause is very complicated. Reference[ IJ

considers that the mainshock and some aftershocks are

maiuly the result of strike and nonnal dislocation based

on the focal mechanism of the mainshock and 34 after-

shocks. However, only a brief discussion of the precise

location of the aftershocks and the frequency-spectrum

analysis are presented in the paper, and no discussion

of the focal nature and type was presented. A totsl of

349 aftershocks are relocated using the double differ-

ence method in this paper, and we discuss the relation-

ship between the distribution of aftershocks and tecton-

ic fault, focal rupture characteristics and seismic type

based on a frequency-analysis of the recorded wave-

No.4 Wu Haiho,~ al.ADalJBit rl the Bado~~g ..V1S. 1 earthquake BOUree characteriatice 17

forms fimn nearby stations.

2 The distribution of the maiushock and

aftershocks

The observed data from the earthquake network of Hu-

bei Province and the induced seismic monitoring net-

work of the Y mgtze Three Gozges :reservoir ( Fig. 1 )

are used to precisely locate the epicenter of the main-

shock via four positioning methods: the simplex meth-

od, HYP2000, hyposat and locSAT. The positioning

:result is presented in table 1 and figure 2. The sta-

tions, are located at an appropriate epicenter dis-

tance, and evenly aUli'Ound the epicenter, were se-

lected for the process of calculation. The result shows

that the cillferences among the positioning results from

the Huhei network are obviously greater than for the

result from the Three Gorges network; the horizontal

error of the positioning results from the Three Gorges network is Jey than 0. 3 km, and the focal depth is

5. 5:t0. 5 km. A total of 349 aftershocks of magnitude Ml ~ 1. 0

from Dec. 16 in 2013 to Mar. 15 in 2014 are relocated

via the double difference method. The ClWital velocity model refezs to the result of litezature['·"J, which in-

cludee a 6-layer structure; the top layer depth is 0, 2,

5 , 8, 11 and 25 km, with a P wave velocity of 5. 2, 5. 5, 5. 9, 6. 1 , 6. 3 and 6. 9 km/s, respectively. U-sing the reconled wavefonDs of 15 stations of the Three

Gorges network, which are located in the range of 10 to

120 km from the epicenter, in the calculation, we fi-nally achieve the high-precision positioning results of

299 aftershocks ( Fig. 3) ; the horizontal error is 30-

80 m and the vertical ermr is 80-150 m.

31.4"N ,----..,-----y----,---~, --,---.,----,

Pure-shape

Hyp2000

HJP0881

LocSAT

Average

F'~g~~re 1 Dittributiou of the fauiiB Rlld tbe lltlltioM ( F 1 : Gaoqiao fault, F 2 : Da-

r»nn fault, F3 :Zboujiuhan-Niukou fault, F, :Maluchi fault)

Table 1 Bpil:aJia' locatioDs of the malnsbock accon1iq to four pasiticJIIIq metllocls

Hubei network 11uee Gorges network

l.&~tude Lalitude ~ Re.idwd ~tude Latitude ~ 0) (0) ) (0) 110.44 31.08 5.7 0.463 110.42 31.09 5.2

110.43 31.08 0.421 110,41 31.09 6.1

110.44 31.10 s.s 0.484 110.42 31.09 s.s 110.44 31.08 5.9 0.446 11o.41 31.09 5.1

110.44 31.09 5.7 110.42 31.09 s.s

Reeidual

0.186

0.110

0.226

0.225

18

2.0km /\~1oyroNo~loyHB • lllmpiolt-.,. c:s liJp20DO c ii:JpOtll

-~ - -• • f • •

•

0

3.0 kill

Pipe 2 f¥ccmtcr 1oc.dono

No.4 19

0,-------~-------.------~----• • • • • A~A' . . .. ~ . .

~ • .:-; . •'.$st''-l>4 tta :.. • 0

l .. s • '\:,. • , , .. . c. ., .·. ·~'l ~ • • • • • • • . • • •• 0 • • • ~ • •• . . ,. . ... -10 ~112~!~ • 0 : . • • • • • • "' • • • ~ •• .cf# • 00 01.1)7

.JS 03-15 • '• • 0

0 F, ~-:s· 0

. . ~ . . ~-S .. .. . ., . f' •• .. lib, ·10 . ij. .. -IS

·S .. ~· 6.j.,0,:". 0

I • et• • •C•' f·' ' o- ' f • • ;-,e.. • 't:1-I • -10 ••• • . g • ~'IS 0 • • ·15

·10 .. .. .. o 0 ..., .. t: ~12-16 • 12-2S

01.o7 03-1S ·IS

-~ 0 ·15

0 s 10 IS ~

(b) Aloolllll.o BB' dl!oolloa

diacriminaled by wavmorm and frequtmcy-spectnd pa-

r:amelen in this papa, that ill, the dominam frequeacy

and the oorner frequency are determined in the focal

spectrum of the reeorded vaveforma of neamy atationa • with the domii14D.t frequency obtained from the Fourier

apectlum and the comer frequeacy obtained from the focal spectrum, which ia calcWated uing the data of

the S-vave 'Window of 10. 24 aeconds. 11le aoiee spec-trum and the insllwllental r:eeponae are removed in the

~18 of the calcu1ation, and the reeuh ill smoothly fihend; the detemrinatiO'\ of the oorner frequency re-fma to the w·2 theon!ltical focal modal The mcmding

waveform of the MHS md MSL lllatiou, which uae short period velocily-aeiamometera w:ilh 50 Hz-10 sec-

ond and are located 16-26lm from the epiOOIIler, are

selected for analysis due tD the factDI'II of the integrity m data, the •zi!!l!rtb and the epicmtml diatance. "'he har-iiiiOntal and vertical Fourier and focal spectra IIJ'e shown in figure 6, and the dcmtinant frequencie• and oorner ~ciee from the ~~peetra are preeented in table 1.

'11lere it a tpcant difference in the oripal re-conlin!! waveform shape between the mainehook ami the

IS

rt;JI.~ . . .. , .. ,:.,. .... . .. ... . ': • • •

• • • •

0. cf.* I _:·? ~ l

. . . "

. "'· .* ,;~· ~ 0 .. . .;:: . : · .. = . .,'P ~ . . . . . . .. . .

C.l Cl ... ' 10 15 :wo ' 10 lS 20 ~) ~ (.) Alooa dlo Ad' Gim:tiOil """""*iaa co !be OOI1iqlllb time

sftmahocb. The wavsfmm of !he ma:inahock., which ill

a£ a l0111er period with simple frequency componenlB and a lack m hip frequency. baa some clwacterilllica a£ tile cal1apae event ( Fig. 5 ( a) ) , but the aftel.'-

ahocka. which exhibit a wide ranp m frequencies and a rich hip frequency specllwD. obviously have aome clwacterilllica of a tectonic eadhquake ( Fig. 5 (b) ) .

As preaented iD table 2, the range a£ the domii14D.t b. quenciee a£ the maiub.ock ill 1. 0 - 4. 5 Hz and tile I'IIIIP' of the comer frequenciet ill 2. 5-3. 5 Hz; howev-er, the J:IUI80 of the dominant frequenciee of the aftel'-ahocka ill wider and up In 15. 0 Hz, and the rail~" of the comer frequencies is 4. 0-7.0 Hz. Compsred with the reauha of refereooe [ 5] , regarding the mainahock,

ita dominant frequency and corner frequency are alight-

ly higher than thcee of the collapse hut are aigoificantly

lower than a Datura! tectonic earthquake of the III!De magllitude, i.e., the majnehock is a hybrid event be-tween a collapee and a Dlltural tectonic earthquake, but the dcmtinant frequency and comer frequency of eaeb aftendaock it accordi111 t.o the result of the 1111tuntl tec-tonic earehquak.e. 'l1ul hmisontal and v6rtical dominant

20 Geodesy and Geodynamics Vol.5

and comer frequencies of 12 events are plotted in the

coordinates , where the abscissa denotes seismic events

and the ordinate denotes the frequency ( Fig. 7 ) . We

can see that the dominant frequency and comer fre-

quency of the mainshock are lower than those of the af-

tershocks, which exhibit a trend of gradually being

higher over time.

A rich high frequency spectrum, obviously have

some characteristics of a tectonic earthquake ( Fig. 5

(b)). As presented in table 2, the range of the domi-

nant frequencies of the mainshock is 1. 0-4. 5 Hz and

the range of the comer frequencies is 2. 5-3. 5 Hz;

however, the range of the dominant frequencies of the

aftershocks is wider and up to 15. 0 Hz, and the range

of the comer frequencies is 4. 0-7. 0 Hz. Compared

with the results of reference [ 5] , regarding the main-

shock, its dominant frequency and comer frequency

are slightly higher than those of the collapse but are

S wave Wmdow

U-D --""",-...1\,"""-"I ' ' ' ' '-------------------'

E-w---"""'r

N-S~ 0 7 14 21 28

(a) Recording waveform of the Ms5.1 mainshock on Dec.16, 2013 at the MHS

35s

significantly lower than a natural tectonic earthquake of

the same magnitude, i.e., the mainshock is a hybrid e-

vent between a collapse and a natural tectonic earth-

quake, but the dominant frequency and comer frequen-

cy of each aftershock is according to the result of the

natural tectonic earthquake. The horizontal and vertical

dominant and comer frequencies of 12 events are plot-

ted in the coordinates , where the abscissa denotes seis-

mic events and the ordinate denotes the frequency

( Fig. 7) . We can see that the dominant frequency and

comer frequency of the mainshock are lower than those

of the aftershocks, which exhibit a trend of gradually

being higher over time.

4 Discussion

1 ) Characteristics of the focal mechanism

The aftershock distribution reflects some features of

0 7 14 21 28

(b) Recording waveform of the Ml3.6 aftershock on Jan. 9, 2014 at the MHS

35s

Figure 5 Comparison of the recorded waveforms of two events at the MHS

xto'

i 15 0 ~ i 10 § -~ 5 ::1!

0

15 x 107

J10 .e 0!

Q 5 il ;>

I 1.8Hz

2 4 6 8 10 12 Frequency(Hz)

(a) Fourier spectrum

14 16

Figure 6

102 10'

10' 10'

-;;- -;;-

'! 10° )10' J10-' l10-' " " rt rt 0! .a 10'' 'fj 10''

No.4

Time

(yy-mm-DDTHH:ss)

2013-12-161'13 :04

2013-12-161'13: 14

2013-12-161'14:36

2013-12-16 16:16

2013-12-161'20:33

2013-12-17'1'20:53

2013-12-19'1'02:56

2013-12-21T20: 18

2014-01-09'1'22:19

2014-01-201'20: 10

2014-01-24T10 :55

2014-02-19'1'21 :13

20

20

s

Wu Haiho,et al.Analysis of the Ba.dang Ms5. 1 earthquake souroe characteristics 21

Table 1 Results of the frequeucy-spectrum analysis

I.ooation epicenter Dominant frequency( Hz) corner frequency{ Hz) Magnitude (Ml)

station --------------------

5.4

3.0

2.6

2.9

2.5

2.9

3.2

2.6

3.6

3.6

2.5

2.5

(km)

MHS 19

MSL 25

MHS 17

MSL 20

MHS 20

MSL 24

MHS 16

MSL 19

MHS 19

MSL 22

MHS 18

MSL 22

MHS 15

MSL 20

MHS 18

MSL 22

MHS 18

MSL 25

MHS 21

MSL 26

MHS 21

MSL 27

MHS 19

MSL 25

3 5 7 9 11

Seismic event(N) (a) Horizonlal COIIlpOill!lll at MUS

ttHtiiittH 3 s 7 9 1l

Seismic event(N) (c) Horizolltal. component at MSL

Horizontal

1.0-4.5

1.0-4.0

2.0-7.5

1.5-6.0

3.0-8.0

2.0-8.0

2.0-8.0

1.5-8.0

3.0-14.0

1.5-8.0

2. 5-12.0

1.5-7.0

2.0-8.0

1.5-7.0

2.0-11.0

1.5-6.5

2.1-15.0

1.5-8.0

2.1-11.0

1.5-8.0

2.0-11.0

1.5-8.5

1.8-12.0

1.5-8.0

20

20

Vertical Horizontal Vertical

1.0-3. 5

1.0-4.0

1.5-8.5

2.0-6.5

3.0-9.0

2.2-11.0

4.0-9.0

2.0-12.0

3.0-13.0

3. 5-12.0

3.5-9.0

1.5-11.0

2.0-9.5

2. 5-9.0

3.0-13.0

1.5-9.5

1.5-15.0

2. 5-13.0

1.5-7.0

3.3-15.0

2.0-9.0

2.0-10.0

1.5-11.0

3.0-15.0

3.0

3.0

3.5

4.0

4.5

5.0

4.0

5.0

6.5

5.0

6.5

5.0

6.5

5.0

6.5

5.0

6.5

5.5

6.0

5.5

5.5

6.5

5.0

4.5

3 5 7 9 11 Seismic evmtt(N)

(b) VclrticaJ. component at MHS

3 s 7 9 11 Seismic eveut(N)

(d) v..rti

22 Geodesy and Geodynamics Vol.5

the fault plane of the mainshock. In the AA ' depth pro-

file , the long axis of the aftershock distribution is ap-

proximately 70' , and in the BB ' depth profile , the

plane is divided into two sections: B1 and B2. The up-

per section, B1, is mainly formed hy aftershocks at the

west of the mainshock near the Gaoqiao fanlt and ex-

hibits a SSE tendency, but the lower section , B2 , is

mainly formed by aftershocks at the east of the main-

shock near the Zhoujiashan fault and exhibits a NNW

tendency. The transition of the two sections is at a

depth of 5. 5 km, which is the focal depth of the main-

shock. This phenomenon is reflected by the contradic-

tory results of the focal mechanism of the mainshock.

The strike of the slip plane from the focal mechanism

according to the initial polarity method is 107', and

the tendency is SE , which is a normal strike-slip dislo-

cation and is consistent with B1 due to the effect of the

Gaoqiao and Daping faults[']. From the focal mecha-

nism according to the CAP method, the strike is ap-

proximately 70' and the tendency is NW; the focal

mechanism is a strike-slip type with small thrust com-

ponents and is consistent with B2. The Longhuiguang

Ms5. 1 earthquake in 1979, which is located 10 km to

the north -east of this earthquake , is of a sinistral

strike-slip and thrust dislocation ; its mechanism is a

strike of 37' with a NW tendency [o,7 ] , which is simi-

lar to that of this earthquake. Therefore, the result of

the strike-slip and thrust dislocation of the focal mecha-

nism of this earthquake is more reasonable if we ana-

lyze the aftershock distribution.

2) The relationship with tectonic characteristics

The aftershock distribution shows that the AA ' direc-

tion is consistent with the strike of Gaoqiao fanlt and

Daping fault, which reflects that the earthquake is in-

fluenced by two faults and not only by the Daping fault

( Fig. 3) . Two significant slip planes, C1 and C2, are

formed in the AA ' profile ( Fig.4) , and the C1 , which

has a north-east trendency, a dip of approximately

60' , and a depth of 10 km, is located near the Gao-

qiao fanlt. According to geological measurements[s,o] ,

the geological occurrence of the Gaoqiao fault is the

strike of NE50' -60', and the tendency of SE and the

dip of 50' - 80' ; the Gaoqiao fault cuts through the

base rock into the upper crust to a depth of less than 15

km, i.e., C1 is the deep plane of the Gaoqiao fault.

The C2 slip plane , which has a SW tendency, a dip of

70' and a depth of 15 km, is near the Zhoujiashan-Ni-

ukou fault. According to geological measurements[s,oJ ,

the geological occurrence of this fault is the strike of

NE20', the tendency of NW and the dip of 60'-80';

the Zhoujiashan-Niukou fanlt cuts through the upper

crust into the middle crust to a depth of less than

25 km. The depth of the C2 slip plant is obviously dee-

per than that of the C1 slip plane, as shown in figure 4

( c) , and so the formation of C2 is influenced hy the

Zhoujiashan-Niukou fanlt. In addition, C1 and C2 are

mainly formed hy the aftershocks that occurred one

month after the mainshock. This resnlt reflects the fact

that the depths of latter aftershocks gradually become

deeper and highlights the synchronous effect and con-

trol hy the two faults. In short, the pre-aftershocks in

this seismic sequence are shallow earthquakes and are

mainly controlled by the Gaoqiao and Daping fault, but

the later aftershocks become deeper and are affected hy

the Zhoujiashan-Niukou fault.

3) The relationship with Karst

There are some significant differences of the waveform,

frequency-spectrum and spectral parameters between

the mainshock and the aftershocks in the seismic se-

quence. The waveform of the mainshock, which is

composed of simple frequency components and is short

of high frequency , has some waveform characteristics

of the collapse , but the waveforms of the aftershocks ,

which exhibit a wide frequency domain and rich high

frequency components , have the waveform characteris-

tics of a natural tectonic earthquake. From the focal pa-

rameter, the corner frequency of the m.ainshock is sig-

nificantly less than that of aftershocks, and is less than

that of the natural tectonic earthquake with the same

magnitude , when compared with the results of refer-

ence [ 5] . In theory , the comer frequency is related to

the source scale and model : the larger the focal scale

and seismic moment are, the lower the comer frequen-

cy is, due to the calibration relation of the source pa-

rameters in the focal spectrum[lO]. In general, the cor-

ner frequency is closely related to the nature of the

subsurface medium, i.e., the compressive strength and

elastic modulus of the rock become weaker by quite a

degree[ II] , which affects the rupture velocity, the

length of the source and seismic wave velocity, and the

.... of the ....... ~· k1: """""'""9''""1 ID th!a p.apoo, md 11!-'-, duo .,._ _,., r..q-.. q .. lb. •si••lwlr • ......,.! "' tluo ••l>i.SiU

Ito.! 'I! no.n. llo.t'B ...... lei :~;.,. ,. ·• r ... llltJ.,

eftllka r4 ~ m retr wtr::!'t e='"8 1he wutA:tw

""" ....... ~ tlll>l: ~ .. .,_-f Gil

24 Geodesy and Geodynamics Vol.5

and the near-surface microseismic activity will be re-

duced because subsurface strata will reach saturation

due to the permeation of reservoir water over the long

term , but the strength of the induced earthquake in the

deep parts of the fault will be stronger.

8~~~~~~ I 160 4 :g !l150

3 ·i ~1~ ~i 130• 0

2004 2006 2008 2010 2012 2014 Time(year)

Figure 9 The relationship of earthquakes above Ml2. 5 and

the water level of the Three Gorges reservoir

5

2

;[ 0 ·o --- ---- .oe- .o.o8 ____ 9 __ R,o? ___ 9_ v C! ____ ~

ofl -2 g. Q -4

0 00

0

0

-6L-~L-~--~--~---L---L---L--~--~--~

2004

Figure 10

2006 2008 2010 2012 2014 Time(year)

The depth distribution of earthquakes above

Ml2.5

Conclusions

1 ) The precise positions of the mainshock and after-

shocks indicate that the seismic sequence is distributed

as a band along the NEE direction. Aftershocks within

one month of the mainshock are mainly at the west of

the mainshock near the Gaoqiao and Daping fault and

are shallow earthquakes within a depth of 5. 0 km.

However the aftershocks after one month become dee-

per, are significantly formed by the two planes Cl and

C2, and their occurrence is in accordance with that of

the Gaoqiao and the Zhoujiashan faults.

2) The frequency-spectrum and spectral parameter

indicate that the corner frequency of the mainshock is

significantly lower than the corner frequencies of the af-

tershocks and is also lower than that of the natural tec-

tonic earthquake with the same magnitude, which may

be related to the natural change of deep strata due to

the erosion of the reservoir water.

3 ) After analyzing the focal mechanism and the geo-

logical tectonic activity near the epicenter, we consider

that the mainshock, which is related to the activity of

the Gaoqiao and Daping faults, is a reservoir-induced

tectonic earthquake , and the activity of the subsequent

aftershocks is influenced by the Gaoqiao fault and the

Zhoujiashan fault.

4) There is an obvious relationship between the seis-

mic activity near the epicenter and a high water level or

rapid change of water level, but the focal depth exhibi-

ted the trend of becoming greater over time , which re-

flects the effect of infiltration and erosion of the reser-

voir water to regional seismic activity.

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Analysis of the Badong MsS. 1 earthquake source characteristics1 Introduction2 The distribution of the maiushock andaftershocks3 Characteristic of the waveform and frequency-spectrum4 Discussion5 ConclusionsReferences