Lecture - contents
52
1 1. Introduction - Activity; data processing; approach 2. Radon and earthquakes in the DSR 3. Rn as a proxy of subtle geodynamics - other indicators 4. Conclusions and implications Lecture - contents
description
Lecture - contents. Introduction - Activity; data processing; approach Radon and earthquakes in the DSR Rn as a proxy of subtle geodynamics - other indicators Conclusions and implications. Radon - as a geophysical tracer . Ultra trace gas in geogas (== “air” in subsurface porosity) - PowerPoint PPT Presentation
Transcript of Lecture - contents
1
1. Introduction- Activity; data processing; approach
2. Radon and earthquakes in the DSR
3. Rn as a proxy of subtle geodynamics - other indicators
4. Conclusions and implications
Lecture - contents
Radon - as a geophysical tracer
• Ultra trace gas in geogas (== “air” in subsurface porosity)
• Noble gas
• Radioactive
• Easily measurable with high sensitivity using electronic systems
• Extremely large variations in space and in time
• A unique combination a unique tool
3
T0
L/L = 0
L/L=10-7-10-10
T1
Local stress/strain, inducing minute changes in rocks (source), enhances release of radon into the geogas environment.
This radon is available for transfer from source to detector
Detector
Source
Advection
4
Measurement principles
3.82 days 1620 years
U-238 radioactive decay series
SolidGeogas
Detection
Decay → recoil → Rn emanation
5
Earthquakes1900-1990
Monitoring sites along Dead Sea Transform
6
NW Dead Sea• Array of stations covering a 20km sector• Next to main western DSR active fault trace• 1.5m deep in unconsolidated gravel• Monitoring since 1994
Intraplate• Depth: 1.2m & 90m• Massive syenite
Southern sector of DSR• Array of stations covering a 20km sector• Precambrian basement rocks of uplifted
boundary blocks of DSR
Radon monitoring arrays along the Dead Sea Rift (DSR)
7
NW Dead Sea
23W – 23E
19W – 19E
21W
17W
Ramon
Arava marginBGO
Roded
E1, E2, E3
IUI
8
C
High Rn zone
MonitoringRn (gamma) sensorIntegration time: 15 min
1994-2005
9
10
u u
u uu u
Dead Sea
Rn monitoring at 1.2 meter in gravel
Graben fill
Rn on carrier gasU bearing
phosphorite
WE
11
Alpha and gamma co-registration17W - time series
Days since 1.1.19924700 4720 4740 4760 4780
Alp
ha (c
ount
s /1
5-m
inut
es x
10)
0
20
40
60
80
100
120
140
160
Gam
ma
(Cou
nts/
15-m
inut
es, x
1000
)
800
1000
1200
1400
1600
1800
Barasol (alpha)PM-11(gamma)
17W - hour resolutionReference: Day 4690-->
Gamma (Counts/15-minutes, x1000)800 1000 1200 1400 1600 1800
Alp
ha (c
ount
s /1
5-m
inut
es)
0
200
400
600
800
1000
1200
1400
1600
1800
• Radon !
• Geophysical sensitivity - High
12
Radon time series of (gamma radiation) in geogas in gravel at main monitoring site, NW Dead Sea, DSR.
1. Multi-year decrease (relative to stable background originating from solid gravel)2. Seasonal variation3. Multi-day variations (MD) - statistically correlated to earthquakes in the Dead Sea Rift (Steinitz et
al., 2003; see below).
17-west, Daily average
Days since 1.1.921000 1500 2000 2500 3000
Cou
nts
x 10
00
0
100
200
300
400
Days since 1.1.1992
Multi-year, seasonal (and multi-day [MD]) variation signatures and signals
13
Seasonal, Multi-day (MD) and Diurnal Radon Signals (DRS)
• Sites 12 km apart• Next to the main
western boundary fault of DSR
Fit of radon temporal variation signatures in gravel (1.2 m depth), at sites 19W and 23W, located 12 km apart along the main western fault of the the DSR. Fit is aparrent in the annual variation pattern, in discrete RnEv and also in the minordiurnal fluctuations (inset).
Days since 1.1.19921800 1850 1900 1950 2000 2050 2100
Rn
conc
entr
atio
n, K
-cou
nts
(23)
20
25
30
35
40
45
50
Rn c
once
ntra
tion
, K-c
ount
s (1
9)
40
60
80
100
120
140
19
23
A
1935 1940 1945
A
Concordance & correlation of signals
14
NW Dead Sea -15 km sector
Day since 1.1.1992
1935 1940 1945
17W
50
100
150
200
250
300
19W
50
52
54
56
58
60
23W
26
28
30
32
34
36
38
17-W19-W23-W
Correlation of MD radon signals among three sites• Depth: 2 meters• Lithology: gravel
15
A
X Data
2040 2045 2050 2055 2060 2065 2070
Cou
nts/
15-m
inut
es (x
1000
)
50
100
150
200
Signal Smoothed
B
Days since 1.1.1992
2040 2045 2050 2055 2060 2065 2070
Cou
nts/
15-m
inut
es (x
1000
)
-10
0
10
Radon signal at site 17W• 30 days• varying gamma signal in
the geogas. • composed of a multi-day
variation (MD) and a superimposed diurnal signal (DRS).
A – Measured signal and the smoothed signal representing the multi-day variation (MD)
B – Separated diurnal variation
16
Multi-year time series of radon (gamma radiation) in geogas in gravel at main monitoring site, NW Dead Sea, DSR.
17-west, Daily average
Days since 1.1.921000 1500 2000 2500 3000
Cou
nts
x 10
00
0
100
200
300
400
Days since 1.1.1992
Average annual Rn concentration vs. Earthquakes
17
Year
1996 1998 2000 2002 2004
Annu
al a
vera
ge R
n co
ncen
trat
ion
coun
ts/1
5-m
inut
es /
1000
at m
onito
ring
stat
ion
17W
60
65
70
75
80
85
90
Radon
100 150 200 250
-100
-50
0
50
100
150
200
250
300
Magnitude 2 to 3 3 to 4 4 to 5 5 to 5 .3
50 km
3 1 0
3 0 0
3 2 0
3 3 0
1
2
3
4
5
3 5 0
Year
1996 1998 2000 2002 2004
Annu
al a
vera
ge R
n co
ncen
trat
ion
coun
ts/1
5-m
inut
es /
1000
at m
onito
ring
stat
ion
17W
60
65
70
75
80
85
90
Num
ber o
f ear
thqu
akes
in D
ead
Sea
rift
50
100
150
RadonEarthquakes
Annual number of earthquakesin the Dead Sea rift
40 60 80 100 120 140 160
Annu
al a
vera
ge R
n co
ncen
trat
ion
coun
ts/1
5-m
inut
es /
1000
at m
onito
ring
stat
ion
17W
60
65
70
75
80
85
90
NW Dead Sea, 1995-2004:• Average annual Rn concentration • Annual number of earthquakes in the DSF
(IJES 2005)
Conclusion (1994-2004)
Relationship found between:Annual average Rn level
andAnnual number of EQ along DSR
18
400 km
200 km
The relation between
• MD radon signals (at site 17W)
&
• earthquakes along the Dead Sea Transform
For (1994-2004)
Relationship found between:Annual average Rn level
andAnnual number of EQ along DSR
19
M>2M<2
1994-2002
1075 earthquakes ,4.2≥ ML ≥ 0
Dead Searift valley
Arabianplate
Israel-Sinaiplate
TECTONIC SEGMENTS
Earthquake Catalog
Seismological Div., GII
20
Days since 1.1.19921950 1960 1970 1980 1990C
ount
s/15
min
utes
X10
00
50
60
70
80
90
100
(40 Days)
minima
Days since 1.1.19921950 1960 1970 1980 1990C
ount
s/15
min
utes
X10
00
50
60
70
80
90
100
Smoothing: 25-hour sliding average
Days since 1.1.19921900 1950 2000 2050 2100C
ount
s/15
min
utes
X10
00
60
80
100
120
140
Days since 1.1.19921950 1960 1970 1980 1990C
ount
s/15
min
utes
X10
00
50
60
70
80
90
100
Start-time of MD radon signalThreshold: Relative amplitude > 1.9
Extraction “start” of MD Rn signal, time windows, Earthquakes
Bin = time window
21
Correlation between Rn MD signals and EQ in DSR (Geology 2003)
For: ML>=2 RA = 1.9
Days after start-time of MD radon signal-15 -12 -9 -6 -3 0 3 6 9 12 15
Num
ber o
f ear
thqu
akes
0
10
20
30
40
5%
1%
0.1%
0.01%
Expected
8 Years: 1995-2002
No. EQ(ML≥2): 165
22
(Steinitz, Begin, Gazit-Yaari, Geology 2003)
Timing of 165 earthquakes (ML2) in the pull-apart grabens of the Dead Sea Rift (Dead Sea, Hula+Kinneret) – relative to the start-time of a radon MD signal.
Earthquakes are clustered in the 0-3 days after the start-time of MD Rn signal
Statistical significance -Probability (%) of randomoccurrence
-15-12 -9 -6 -3 0 3 6 9 12 15 D ays af ter S tart- tim e
0
10
20
30
40
Nu
mbe
r of
ear
thqu
akes
1.05.0
0.10.01C
P robability (%) of ran dom occu rren ce
Days after start-time of radon event
Dead Sea, Kinneret and Hula pull-apart
grabensN
umbe
r of e
arth
quak
es
Steinitz et al 2003
23
Previous approach focused on: Counting earthquakes within
multi-day Rn anomalies(Steinitz et al., 2003, Geology 31: 505-508)
New approach focuses on:
Counting days of earthquakes and Rn anomalies
(unpublished)
24
MD-Starts and EQ correlation
Rn time series at 1-hour resolution
Smoothing: 25-hour sliding average
Smoothed time seriesResidual time series
Extraction of MD starts, Amplitude and RAEQ Catalog
Regional sets MD-starts EQqueries
25
1600 1610 1620 1630 1640 1650 1660 1670D ays sin ce 1.1.92
0
40000
80000
120000
160000
200000
Rn
cou
nts/
15 m
in
0
1
2
3
4
Rel
ativ
e am
plit
ude
Rn Start-times
26
1600 1610 1620 1630 1640 1650 1660 1670D ays sin ce 1.1.92
0
40000
80000
120000
160000
200000
Rn
cou
nts/
15 m
in
0
1
2
3
4
Rel
ativ
e am
plit
ude
3 days
Rn Start-times for Relative Amplitude > 1.9
Earthquakes
27
Tectonic segment Radon time-series
Extraction of significant “starts” (n ~ 150)
Expected number of EQ per:a) (1-day)b) 3 & 4 -day time window (bin)
3 & 4 -day time window (bin), Relative to “start”
Count: number of EQ in time window
Histogram: number of EQ in 3 & 4 -day bin
All bins
(EQ in time-bin)n starts
All “starts”
Flowchart for MD-Starts and EQ correlation
Number of EQ in tectonic segment
Number of measurement
days (1995-2004)
28
R n anom aly days1 2 3
D ays since 1.1.92623 624 625 626 627 628 629
R n anom aly starts p .m
R n anom aly days1 2 3
D ays since 1.1.92623 624 625 626 627 628 629
R n anom aly starts a.m
Definition of “Rn anomaly days” for a time bin of n=3after the start time of Rn anomalies
29
A day is characterized by two attributes:
2) It is a day which occurred n days after the start time of a Rn anomaly,with a certain Relative Amplitude (or not)
YN
Y NYN
Y N1) It is a day in which
at least one earthquake (of magnitude ≥ML) occurred (or not)
30
Are these two attributes independent ? Did at least one
earthquakeoccur in day?
Was day withinn days afterstart of Rn anomaly?
)One degree of freedom(Yes No
Yes
No
Total number of days
Observed
ExpectedObserved
Expected
Totalnumberof days
countEQ
(diff)
count day-start
Ntotal
(diff)
Use the 2 test to determine the probability of random occurrence
31
Analyzing the Rn-EQ connection
1. For earthquakes out of the Dead Sea rift valley
D ead Searift va lley
Arab ianplate
S inaiplate
0 to 2 2 to 4.601
Rn monitor
32
Yes No
607 2829
342
3436
Total
Total number of days
Was day within3 days afterstart of Rn anomaly?
Yes
No
For earthquakes 1994-2004, ML >0
Out of the Dead Sea rift valley,Rn anomaly cutoff of Rel. Amp: 2.0 Did at least one
earthquakeoccur in day?
Totalnumberof days
3094
33
Yes No
5760.4
285281.6
550546.6
25442547.4
607 2829
342
3094
3436
Total
Total number of days
Yes
No
ObservedExpected
ObservedExpected
Did at least one earthquakeoccur in day?
Totalnumberof days
Was day within3 days afterstart of Rn anomaly?
For earthquakes 1994-2004, ML >0
Out of the Dead Sea rift valley,Rn anomaly cutoff of Rel. Amp: 2.0
35
Yes No
5760.4
285281.6
550546.6
25442547.4
607 2829
342
3094
3436
Total
Total number of days
Yes
No
ObservedExpected
ObservedExpected
[2] = Σ 0.19
Did at least one earthquakeoccur in day?
Totalnumberof days
Was day within3 days afterstart of Rn anomaly?
For earthquakes 1994-2004, ML >0
Out of the Dead Sea rift valley,Rn anomaly cutoff of Rel. Amp: 2.0
* Including the Yates continuity correction
*
One degree of freedom
36
Yes No
5760.4
285281.6
550546.6
25442547.4
607 2829
342
3094
3436
Total
Total number of days
Yes
No
ObservedExpected
ObservedExpected
[2] = Σ 0.19
Did at least one earthquakeoccur in day?
Totalnumberof days
Probability of random occurrence = 0.66No significant connection
Was day within3 days afterstart of Rn anomaly?
For earthquakes 1994-2004, ML >0
Out of the Dead Sea rift valley,Rn anomaly cutoff of Rel. Amp: 2.0
37
Analyzing the Rn-EQ connection
2. For earthquakes within the Dead Sea rift valley
D ead Searift va lley
Arabianplate
S inaip late
0 to 2 2 to 4 .601
Rn monitor
38
Yes No
6649.2
276292.8
428444.8
26662649.2
494 2942 3436
Total
Total number of days
Yes
No
ObservedExpected
ObservedExpected
For earthquakes 1994-2004, ML >0
Within the Dead Sea rift valley,Rn anomaly Relative Amplitude > 2.0 Did at least one
earthquakeoccur in day?
Totalnumberof days
Was day within3 days afterstart of Rn anomaly?
342
3094
39
Yes No
6649.2
276292.8
428444.8
26662649.2
494 2942 3436
Total
Total number of days
Yes
No
ObservedExpected
ObservedExpected
Did at least one earthquakeoccur in day?
Totalnumberof days
Was day within3 days afterstart of Rn anomaly?
342
3094
[2] = Σ 7.03
For earthquakes 1994-2004, ML >0
Within the Dead Sea rift valley,Rn anomaly Relative Amplitude > 2.0
40
Yes No
6649.2
276292.8
428444.8
26662649.2
494 2942 3436
Total
Total number of days
Yes
No
ObservedExpected
ObservedExpected
Did at least one earthquakeoccur in day?
Totalnumberof days
Was day within3 days afterstart of Rn anomaly?
342
3094
Probability of random occurrence = 0.008Significant connection
For earthquakes 1994-2004, ML >0
Within the Dead Sea rift valley,Rn anomaly Relative Amplitude > 2.0
41
Analyzing the Rn-EQ connection
D ead Searift va lley
Arabianplate
S inaip late
0 to 2 2 to 4 .601
Rn monitor
We now test a Rn-earthquake connection within the Dead Sea rift valley
for 3 days before the start time of Rn anomalies
42
Yes No
5548.5
282288.5
439445.5
26602653.5
494 2942 3436
Total
Total number of days
Yes
No
ObservedExpected
ObservedExpected
Did at least one earthquakeoccur in day?
Totalnumberof days
Was day within3 days beforestart of Rn anomaly?
337
3099
[2] = Σ 0.98
For earthquakes 1994-2004, ML >0
Within the Dead Sea rift valley,Rn anomaly Relative Amplitude > 2.0
43
Yes No
5548.5
282288.5
439445.5
26602653.5
494 2942 3436
Total
Total number of days
Yes
No
ObservedExpected
ObservedExpected
Did at least one earthquakeoccur in day?
Totalnumberof days
Was day within3 days beforestart of Rn anomaly?
337
3099
Probability of random occurrence = 0.32No significant connection
For earthquakes 1994-2004, ML >0
Within the Dead Sea rift valley,Rn anomaly Relative Amplitude > 2.0
44
M>2M<2
10 years; 1994-2004
Earthquakes,4.2≥ ML ≥ 0
Twelve 4-day time bins around “start”
Dead Searift valley
Arabianplate
Israel-Sinaiplate TECTONIC SEGMENTS
DSROUT-of-DSR
45
Testing for correlation between Rn MD signals and EQ in DSR
Earthquakes: ML≥0; ML≥2
10 Years
(1995-2004)
DSROUT-of-DSR
RA = 1.8; 2.0 bins: 4 daysspan: -24 to +24 days
relative to “start”
Observed no. of earthquakes & Expected number
Enrichment of earthquakes
Testing the statistical significance of enrichment
OrProbability that correlation is a random one
(using the 2 criterion)
46
Observed - Expected
ML >=0 ML >=0
ML >=2ML >=2
Observed/Expected no. of EQ in DSR, ML >=0
Time bin relative to START-24 -20 -16 -12 -8 -4 0 4 8 12 16 20 24
Obs
erve
d nu
mbe
r
0
20
40
60
80
100
120
140 RA > 1.8RA > 2 Expected >1.8Expected >2
Observed/Expected no. of EQ in OUT-of-DSR, ML >=0
Time bin relative to START-24 -20 -16 -12 -8 -4 0 4 8 12 16 20 24
Num
ber
0
20
40
60
80
100
120
140 RA > 1.8RA > 2 Expected >1.8Expected >2
Observed/Expected no. of EQ in OUT-of-DSR, ML >=2
Time bin relative to START-24 -20 -16 -12 -8 -4 0 4 8 12 16 20 24
Num
ber
0
10
20
30
40
50RA > 1.8RA > 2 Expected 1.8Expected 2
Observed/Expected no. of EQ in DSR, ML >=2
Time bin relative to START-24 -20 -16 -12 -8 -4 0 4 8 12 16 20 24
Num
ber
0
10
20
30
40RA > 1.8RA > 2Expected >1.8Expected >2
47
Enrichment of EQ OUT-of-DSR, ML >=0
Time bin relative to START-24 -20 -16 -12 -8 -4 0 4 8 12 16 20 24
Enr
iche
men
t (%
)
-20
-10
0
10
20RA > 1.8RA > 2
Enrichment
Enrichment of EQ OUT-of-DSR, ML >=2
Time bin relative to START-24 -20 -16 -12 -8 -4 0 4 8 12 16 20 24
Enr
iche
men
t (%
)
-20
0
20
40RA >1.8RA >2
Enrichment of EQ in DSR, ML >=0
Time bin relative to START-24 -20 -16 -12 -8 -4 0 4 8 12 16 20 24
Enr
iche
men
t (%
)
-10
0
10
20
30
40
50
RA > 1.8 RA > 2
Enrichment of EQ in DSR, ML >=2
Time bin relative to START-24 -20 -16 -12 -8 -4 0 4 8 12 16 20 24
Enr
iche
men
t (%
)
-20
0
20
40
60
80RA > 1.8RA > 2
48
Statistical significance
Probability for random correlation in OUT-of-DSR, ML >=0
Time bin relative to START-24 -20 -16 -12 -8 -4 0 4 8 12 16 20 24
Chi
2
0
2
4
6
8
10
12
14 RA > 1.8RA > 2
1%
0.5%
0.1%
5%
Probability for random correlation in OUT-of-DSR, ML >=2
Time bin relative to START-24 -20 -16 -12 -8 -4 0 4 8 12 16 20 24
Chi
2
0
2
4
6
8
10
12
14 RA >1.8 RA > 2
1%
0.5%
0.1%
5%
Probability for random correlation, in DSR, ML >=0
Time bin relative to START-24 -20 -16 -12 -8 -4 0 4 8 12 16 20 24
Chi
2
0
2
4
6
8
10
12
14 RA > 1.8RA > 2
1%
0.5%
0.1%
5%
Probability for random correlation in DSR, ML >=2
Time bin relative to START-24 -20 -16 -12 -8 -4 0 4 8 12 16 20 24
Chi
2
0
2
4
6
8
10
12
14 RA > 1.8RA > 2
1%
0.5%
0.1%
5%
49
Conclusions:Earthquakes within the Dead Sea rift valley(but not out of it)• significantly occur within several days after the start
of Radon anomalies,as recorded in the Dead Sea 17W monitor,(but not before them)
[ The daily probability of earthquake occurrence in “Rn-Anomaly days” increases with the increase in the cutoff valueof Relative Amplitude of the Rn anomalies ]
50
Preliminary explanation
1. A transient strain causes increase in Rn flux near the 17W monitor.
2. This strain may cause an earthquake to occur
several days later, somewhere within the Dead Sea rift valley.
3. The higher the strain, the higher is the transient Rn flux, and the higher is the probability of an earthquake occurrence in “Rn anomaly” days, relative to other days.
51
Summary of results of 10 years of high-resolution Rn monitoring:
52
1. This study presents a significant statistical relationship between Rn flux and earthquakes that occur within the same tectonic provinceon an annual basis.
2. This study also presents a significantstatistical relationship between Rn anomalies and earthquakesthat occur after the start time of the anomalieswithin the same tectonic province.
53
END
Thank You
