Earthquake Research in China
Volume 25，Number 3，2011
The Influencing Factors of Escaped
Radon from the Jiayuguan Fault
Zone and Its Earthquake
1
Reflecting Effect
Wang Bo，Huang Fuqiong，and Jian Chunlin
China Earthquake Networks Center，Beijing 100045，China
The paper analyzes the radon data of nearly two decades on the Jiayuguan fault zone，
discusses the main influencing factors，and puts forward the relationship between radon
and air temperature，ground temperature and rainfall． We summarized the earthquake
reflecting effect for M L ≥5. 0 about 400km within the Jiayuguan station，and reached the
conclusion that it has better earthquake-reflecting ability before an earthquake，usually
appearing as abnormal changes in sustained low value． By extracting the annual trend of
radon in Jiayuguan station over many years，we discovered that the annual trend of radon
has a close relationship with the seismic activity in surrounding areas，namely，if the
annual variation of radon is larger，the seismic activity in surrounding areas is stronger；
Otherwise，if the annual variation of radon is relatively stable，the seismic activity in the
vicinity is weak．
Key words： Jiayuguan station； Fault Gas； Radon； Earthquake Precursor
INTRODUCTION
Radon is a decay product of radioactive uranium，radium and thorium in the earth's crust．
Since the discovery of the relationship between the variation of concentration of escaped radon gas
in the soil above faults and the earthquake activity in the 1970s， the use of gas radon
concentration anomalies to monitor seismic activity has been more widely applied by many
researchers （ King，1978，1980； Wang Chengmin et al． ，1991； Shi Yong et al． ，1993； Yu
Wenxin et al． ，1995； Zmazek et al． ，2003） ．
Since the observation of gas radon on the Jiayuguan fault in 1989，considerable information
has been accumulated． Years of observation show that the radon concentration in the measuring
1
Received on February 2，2010． This project was sponsored by the Youth Fund of China Earthquake Networks
Center （150-1548，406-1503） ．
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359
point has a good periodicity， and has a better earthquake-reflecting ability before strong
earthquakes in the western part of the Qilian Mountains and its surrounding region． He Genqiao et
al． （ 1994 ） made a comprehensive analysis on the changes and cross-fault measurements of
escaped radon on the Jiayuguan fault before the M5. 4 earthquake on January 12，1992 in
southern Gansu and found that both changes were consistent，thus confirming the variation of
escaped radon as a reliable earthquake precursor． Zhang Yu et al． （ 2004 ） analyzed the
correspondence between the earthquake and annual variation of radon anomalies in Jiayuguan
before several strong earthquakes and through comparative analysis of radon data in Jiuquan
station，reaching the conclusion that soil gas radon in Jiayuguan fault has a better earthquake
reflecting effect．
So far research has been limited to a simple analysis of data after the earthquake． More indepth analysis and research is needed on the main influencing factors of the variation of escaped
radon concentration， as well as the relationship between this abnormality and earthquake
preparation and occurrence． This paper collected data from gas radon，air temperature，rainfall，
ground temperature and other observations in the station from 1998 to 2009，systematically
analyzed the main influencing factors of radon concentrations and discussed the annual trends and
seismic activity in surrounding areas so as to provide a reliable criterion for identification of future
earthquake precursors．
1
BACKGROUND AND OBSERVATION DATA OF JIAYUGUAN STATION
The gas radon observation site on Jiayuguan fault is located about 2km （39°49'23″N，98°
13'19″E） south of Jiayuguan station． Sampling hole depth is about 2. 4m （ the radon data of the
Jiayuguan fault in the paper is the data from the main sampling hole） ． The site has an elevation of
1716m，surrounded by desert and hills，crossing the Jiuquan basin between the southern marginal
fault of the Alaxa block and the northern marginal fault zone of the Qilian Mountains． The
Jiayuguan fault is a high-angle thrust fault，striking N35°W，dipping SW at dip angle 80° ～ 90°，
with displacement of 1200m ～ 1600m （ Fig． 1（ a） ） ．
Observation instrument is the FD-125 analysis instrument for radon and thorium
measurement． Gas radon is sampled with a diffusion vacuum cylinder． The gas is extracted from
the sample cylinder and injected into the negative pressure scintillation chamber using a syringe，
then mixed with a fixed volume of uncontaminated air． Upon standing for 1 hour，it is measured
once each morning with the FD-125 analysis instrument for radon and thorium measurement．
The paper used gas radon data from 1998 to 2009 in the Jiayuguan fault and selected
corresponding multi-auxiliary information，such as temperature，ground temperature，humidity，
air pressure and rainfall （ Fig． 2） ． Earthquake catalog was selected from the China Earthquake
Networks Center Express catalog．
2
2. 1
ANALYSIS OF OBSERVATIONAL DATA
Influencing Factors
In general，the change of gas radon concentration is caused by many factors，such as the
opening and closing of the fault，the depth of the sampling hole，the ground temperature changes，
diurnal variation and annual variation of air pressure and temperature and rainfall． Seasonal
changes of temperature can cause changes of air pressure， ground temperature， ground-air
exchange rate，cyclical changes in observational instruments． Changes in ground temperature may
also cause cyclical changes in thermo-elastic strain of near-surface rocks，and as a result，the gas
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Earthquake Research in China
Fig. 1
（ a） Sketch map of regional geological structure in Jiayuguan （ adapted from the 1∶ 200，
000
regional geological map） （ Institute of Geology，State Seismological Bureau，1993） ；
（ b） The environment of the Jiayuguan fault gas radon observation chamber；
（ c） Sampling hole of gas radon on Jiayuguan fault
radon concentration changes periodically （ Du Jianguo et al． ，1998） ． These factors cause regular
and irregular annual variation and mutation of the fault gas radon，and the measured value of the
annual variation may also be different due to the different locations of the specific observation
sites．
From the variation pattern over years we can see （ Fig． 2） ，gas radon in the Jiayuguan fault
has an apparent annual trend． The measured value is higher in summer and lower in winter，
similar to the trend of ground temperature variation． In order to figure out the main influencing
factors，and distinguish changes related to the fault-activities and other interfering factors，
combined with previous studies，this article analyzes the impact of air temperature，ground
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361
Fig. 2
Observation curves of each measuring item from 1998 to 2009 in the Jiayuguan station
temperature and rainfall on the radon value．
2. 1. 1
The Relationship between Gas Radon and Air Temperature
Fig． 2 shows that the change in radon on the Jiayuguan fault has a good annual trend，
following a pattern of being high in summer and low in winter，very similar to the trend of air
temperature change． Fig． 3 shows the relationship between radon and air temperature． There is a
good linear correlation between the two．
Fig. 3
Relationship between the temperature and the
monthly radon value in the Jiayuguan station
In order to analyze the correlation of radon and air temperature in a long period，we used
Fourier's moving average method to extract the long-period component of radon value variation
（ annual change period） ，that is，the annual estimated value （ Fig． 4） ．
In order to eliminate the direct effects of seismic activity on radon concentration，we selected
the radon data from 1998 to 2000，during which there was less earthquake activity，to perform the
analysis． First we normalized temperature and annual estimated value of radon to eliminate the
Earthquake Research in China
362
Fig. 4
Annual estimated value of gas radon in the Jiayuguan station
impact of annual amplitude variation on the analysis of the correlation between the two． The
results show （ Fig． 5 ） that the annual estimated value of radon is consistent with the annual
change of air temperature， and there is a good correlation between them with correlation
coefficient 0. 94． This indicates that the annual variation of radon gas on the Jiayuguan fault may
be mainly affected by changes in air temperature and the short-term mutation may be affected by
other factors （ rainfall，seismic activity，etc． ） ．
Fig. 5
Relationship between annual estimated value of radon and air temperature the in Jiayuguan station
2. 1. 2
Relationship between Ground Temperature and Radon
Du Jianguo et al． （1998） investigated the correlation between the radon concentrations on
the Babaoshan fault and ground temperature at the depth of 3. 2m and found that there is no
obvious correlation between the escaped radon and geotherm． We consider this is because there
are many factors affecting the radon observation or perhaps due to the lag of ground temperature
change． To further analyze the relationship between radon concentration and ground temperature，
the author also selected observation data of gas radon on the Jiayuguan fault from 1998 to 2000．
First，we normalized ground temperature and annual estimated value of radon to eliminate the
impact of annual amplitude variation on the analysis of correlation between the two． The results
（ Fig． 6） ，show ground temperature change lagged a period of about 85 days behind the annual
radon change． It is concluded by the delay analysis that the maximum correlation coefficient is
0. 97．
To find out whether the ground temperature has a similar hysteresis with the air temperature，
the authors used the same method to analyze the relationship between the air temperature and the
ground temperature in Jiayuguan station，the maximum correlation coefficient is 0. 96，the annual
change of ground temperature lags about 82 days behind the air temperature （ Fig． 7） ．
The above analysis shows that the delay of annual change of the air temperature due to
ground temperature is quite similar to that of radon，which also confirms that the annual change of
radon in value is mainly affected by temperature． Compared to air temperature， ground
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363
Fig. 6
Relationship between annual estimated value of radon and
ground temperature in the Jiayuguan station
Fig. 7
Correlation diagrams of air temperature and
ground temperature in the Jiayuguan station
temperature is less affected by other environmental factors and the annual change is smaller． The
annual air temperature trend is similar to that of the ground temperature as the lag days are often
associated with rock thermal conductivity of the observation sites and are relatively fixed． Thus，
we can also calculate the number of days that the annual trend of ground temperature lags behind
the air temperature as a complementary analysis tool in determining the relationship between
annual changes of the escaped fault gas radon and air temperature．
2. 1. 3
The Relationship between Soil Moisture and Fault Gas Radon
Soil moisture is another major factor that affects fault gas radon． Experimental data between
soil moisture and soil radon indicate that （ Hou Yanzhen，1994） ，when water content in the soil
is low，the fault gas radon concentration increases with increased soil water content； but when soil
moisture is saturated or close to it，the fault gas radon concentration is significantly reduced． Zhu
Ziqiang et al． （ 1991 ） compared radon data before and after heavy rain on the same fault of
Babaoshan Fault and found that after the rainfall gas radon decreased significantly．
In the absence of soil moisture data，the authors analyzed relationship between the rainfall
Earthquake Research in China
364
and atmospheric humidity and radon and found poor correlations among them． However，this is
not in contradiction with the experimental data． Soil moisture is not simply affected by rainfall，
but also related to soil water-holding capacity，surface evaporation rate and other factors． In
addition，the Jiayuguan fault radon is generally not sampled immediately after the rainfall，so we
could not draw a relationship between radon and rainfall． Future experiments or field tests are
needed for verification．
2. 2
Analysis of Earthquake Reflecting Effect
The period before an earthquake is often accompanied by the buildup of crustal stress，
increased fault activity and change of rock porosity，which may lead to changes in gas content or
increase of gas migration． If the underground aquifer deforms under stress，it will accelerate the
movement of gas，enhancing the diffusion of radon gas，and thus lead to changes in radon levels．
Thus the determination of radon changes on the fault can serve as an earthquake precursor （ Wang
Yongcai，1992； Liu Yaowei et al． ，2006； Zhao Jun et al． ，2009） ．
We selected 24 earthquakes with M L ≥ 5. 0 from 1989 to 2009 within the range of 93° ～
102°E，37° ～ 42°N，of which，19 are of M L 5. 0 to 5. 9 ，and 5 are of M L6. 0 to 6. 9 （ Fig． 8） ．
Fig. 8
Epicenters distribution of M L ≥5. 0 earthquake near the
Jiayuguan station （93° ～ 102°E，37° ～ 42°N）
From the spatial distribution，these earthquakes are mainly distributed along two directions：
one is along the northern margin of the Qilian Mountains and Jiayuguan fault，the other is near the
Delingha Dachaidam-Zongwulong Mountain fault． From the temporal distribution， these
earthquakes occurred between 1991 and 1993，2001 and 2004，and from the second half of 2008
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365
to the present．
We carefully analyzed and summarized the relations of escaped radon variation with
magnitude and epicentral distance before each earthquake on the Jiayuguan fault （ Table 1 ） ．
Associated with the previous cases of earthquake-reflecting effect at Jiayuguan station （ Zhang Yu
et al． ，2004； Cao Xi，et al． ，2008） ，we re-summarized and organized the observations of the
station． The earthquake-reflecting effect of radon concentration on the Jiayuguan fault can be
classified as the following three types： ① Rapid decline． Earthquake occurs when the
measurements keep low （ Fig． 9 （ a ） ） ． ② Earthquake occurs when the low-value anomaly is
broken （ Fig． 9 （ b） ） ． ③ Earthquake occurs when multiple sudden changes in high-value and
abnormal annual variation in the high value occur （ Fig． 9 （ c） ） ． We found that this station is
more sensitive to the surrounding seismicity and the majority of abnormalities ended immediately
before or after the earthquake． For some events with continuous anomalies，they were mostly
related to the subsequent earthquakes．
Fig. 9
Classification of earthquake-reflecting effect of the radon gas anomaly in the Jiayuguan station
The analysis shows that the vast majority of these earthquakes were within 400km from the
Jiayuguan station． Among the 24 earthquakes，most earthquakes were preceded by the anomalies，
with the only exception of the low value anomaly in 1995 which was followed by an earthquake．
The radon concentrations were normal before some earthquakes on the Jiayuguan fault，but
obvious abnormalities occurred before 20 earthquakes，accounting for 83% of the total earthquake
number． For example，the seismicity near Delingha was active in 2004，and there were several
earthquakes of M5. 0． The overall trend of fault gas radon in the Jiayuguan fault zone broke
through the annual variation in 2003 and 2004，abnormal high-value jumps appeared，and after
the Delingha M5. 9 earthquake in May 11，the radon concentrations were significantly low in July，
August and September，which may be related to the multi seismic activities throughout the region．
Such situations reoccurred after the Wenchuan earthquake．
Considering the epicenter distance in analyzing the relationship between seismic activity and
radon，it can be seen that within the 200km，the abnormalities behave mainly as rapid decline，
and then the anomaly was displayed as a sustained low value or slightly turning upward． Within
200km ～ 300km，the anomalies were mainly responses to the earthquakes in the vicinity of
Delingha，shown as abnormal annual variation with sudden changes in high value． If the value
remained low，the range of earthquake preparation might be larger，as in some of the strong
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366
Table 1 Parameters of the moderate and strong earthquakes and short-term radon anomalies near
the Jiayuguan station
Occurrence
time
Epicenter
1991-01-02
SW Qilian
φ
/ °N
λ
/ °E
ML
Maximum
Epicentral
Abnormal
amount of
distance
duration
abnormal
（ km）
（ d）
（ Bq / L）
Characteristics
1992-01-12
Jiayuguan
39. 7 98. 3 5. 4
15
－ 14. 7
80
1992-06-21
Sunan
Northern
Golmud
Tulai
Sunan county
Qiqing town
38. 5 99. 5 5. 0
183
—
—
Rapid decline，
sustained low value
Abnormal annual
variation，the measured
value is low
Abnormal annual
variation，low value
Rapid decline，
sustained low value
Obscure abnormalities
37. 1 94. 7 5. 1
430
—
—
Obscure abnormalities
38. 6 98. 7 6. 0
142
—
—
39. 2
5. 3
71
16
18
1991-09-02
1991-10-01
1993-09-05
1993-10-26
NW Haixi
Xitieshan
Mountain
Menyuan
Qinghai
38. 2 99. 9 5. 1
231
15
68
37. 3 95. 4 5. 1
372
－ 18. 5
150
37. 8 101. 4 5. 2
355
－ 20
180
2002-12-14
Yumen
39. 8 97. 3 5. 9
78
30
150
2003-04-17
Delingha
37. 5 96. 8 6. 6
285
35. 6
70
2003-10-25
Minle，
Shandan
38. 4 101. 2 6. 1
301
20
210
2003-10-25
Minle，
Shandan
38. 4 101. 1 5. 8
294
20
210
2004-02-25
Delingha
37. 6 96. 7 5. 0
279
14
16
2004-03-17
Delingha
37. 6 96. 7 5. 2
279
15
37
2004-05-04
Delingha
37. 5 96. 7 5. 5
289
15
85
2004-05-04
Delingha
37. 5 96. 7 5. 1
289
15
85
2004-05-11
Delingha
37. 5 96. 7 5. 9
289
29
90
2008-03-30
Sunan
5. 0
384
—
—
2008-11-10
Haixi
37. 6 95. 9 6. 3
318
20
95
2009-08-28
Haixi
37. 6 95. 8 6. 4
324
13
28
2009-08-31
Haixi
37. 6 95. 8 5. 9
324
13
31
2009-11-05
Haixi
Hami county，
Xinjiang
Delingha
37. 6 95. 8 5. 1
324
13
95
Obscure abnormalities
Abnormal annual variation，
low value
Abnormal annual variation，
abnormal high value
Abnormal annual variation，
sudden high-value change
Abnormal annual
variation，sudden
high-value change
Abnormal annual variation，
sudden high-value change
Abnormal annual variation，
sudden high-value change
Abnormal annual variation，
sudden high-value change
Abnormal annual variation，
sudden high-value change
Abnormal annual variation，
sudden high-value change
Abnormal annual variation，
sudden high-value change
Obscure abnormalities
Rapid decline，sustained
low value
Abnormal annual variation，
low value
Abnormal annual variation，
low value
Sustained low value
41. 9 94. 5 5. 1
388
13
135
Sustained low value
37. 5 96. 7 5. 0
289
13
141
Sustained low value
2001-07-11
2009-12-14
2009-12-21
38
98
102
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367
earthquakes in the Haixi region of Qinghai and Hami county in Xinjiang mentioned in the paper．
The above analysis shows that escaped radon in Jiayuguan fault is mainly affected by air
temperature，so the measured values of air temperature in Jiayuguan can be used to estimate the
annual trend of radon． After the removal of the annual variation of radon，this paper did the fitting
analysis and used the general polynomial curve fitting method． Results were shown in Fig． 10． It
can be seen from the figures that the annual trend of radon gas from 1991 to 1994 undulated，was
steady from 1996 to 1999，and undulation began to increase from 2000 to 2004． Meanwhile，the
seismicity began to be active in the vicinity of Jiayuguan station．
Fig. 10
（ a） Radon concentration in Jiayuguan fault （ after removing the annual periodic change） ；
（ b） General polynomial fitting curve； （ c） Residual； （ d） M-t map of M L ≥5. 0 earthquakes
near Jiayuguan station； （ e） Frequency graph of M L ≥5. 0 earthquake near the Jiayuguan station
In more than a year after the Wenchuan Earthquake in 2008，the low-value phenomenon in
observations of radon concentrations of the Jiayuguan fault occurred many times，and a number of
strong earthquakes occurred in Haixi and Delingha and other places． From the variation trend of
multiple years，we can see the curves continued to decline，and the amplitude of annual variation
of radon began to increase，this may mean a new round of strong earthquakes in the vicinity would
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Earthquake Research in China
become active． Therefore，in the next one to two years，there is the possibility of strong
earthquakes in a radius of 400km around the Jiayuguan station．
3
CONCLUSION AND DISCUSSION
Through analysis of the influencing factors of the escaped radon from Jiayuguan fault zone
and its earthquake reflecting effect，we can draw the following conclusions：
（1） The variation in radon concentrations on the Jiayuguan fault has a better earthquakereflecting effect for earthquakes of M L ≥5. 0 in a range about 400km distance from the Jiayuguan
station．
（2 ） The radon concentrations on the Jiayuguan fault show an evident annual variation
feature，and we discovered that the annual trend of radon change has a close relationship with that
of air temperature． It can be concluded that the annual trend of radon is controlled by annual
trends of air temperature，and its short-term mutations may be associated with seismic activity，
rainfall and other factors．
（3） Precursory anomalies of gas radon on the Jiayuguan fault mainly behaved a sustained low
value anomaly，but there was also a high-value abnormality which generally corresponded to
earthquakes at the south of Jiayuguan station，and continuous low value would indicate that the
seismogenic zone may be larger．
（4） In the trend of radon variation of years in Jiayuguan station，if the annual variation of
radon is larger，the seismic activity in surrounding areas is stronger； otherwise，the annual
variation of radon is relatively stable，the seismic activity in the vicinity is weak． Thus we believe
that in the next two years，seismic activity may be more active in the region near Jiayuguan
station，there will be strong earthquakes，and there is high possibility of string earthquakes．
In analyzing main influencing factors of radon concentrations in Jiayuguan，this paper only
performed correlation analysis on the meteorological factors． During data processing of the annual
trend of radon in Jiayuguan fault，we only eliminated the temperature effects，because its
relationship with the ground temperature，rainfall and etc． is not clear，so we did no further
treatment． In-depth analysis is still in need．
The importance of escaped gas from faults to earthquake monitoring and prediction is clear．
This paper analyzed the main influencing factors and put forward the relations between radon and
air temperature，ground temperature，rainfall． The results are useful for a better understanding of
the extraction of the precursor abnormal variations related to seismic activity and also provide basis
for the in-depth analysis of the relationship between fault movement and fault escaped gas．
ACKNOWLEDGEMENTS
Thanks to Cao Lingling，research associate in Earthquake Administration of Gansu Province，
senior engineer Zhang Yu and researchers in Jiayuguan station for providing the observational
data． Thanks to Dr． Zhou Longquan for providing help in data processing，and to the reviewers
for pertinent comments and suggestions on this paper．
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About the Author
Wang Bo，born in 1984，graduated from the Institute of Crustal Dynamics，CEA，2008，and
now works at the China Earthquake Networks Center． Major research interests include
hydrodynamics and earthquake prediction study． E-mail：wangbo313@ 163． com