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 T0T0  L/L = 0   L/L= T1T1 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 days1620 years U-238 radioactive decay series Solid Geogas Detection Decay → recoil → Rn emanation

5 Earthquakes 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 A Ramon Arava margin BGO Roded E1, E2, E3 IUI

8 C High Rn zone Monitoring Rn (gamma) sensor Integration time: 15 min

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10 uu uu uu Dead Sea Rn monitoring at 1.2 meter in gravel Graben fill Rn on carrier gas U bearing phosphorite WE

11 Alpha and gamma co-registration 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 variation 3.Multi-day variations (MD) - statistically correlated to earthquakes in the Dead Sea Rift (Steinitz et al., 2003; see below). Days since 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 Concordance & correlation of signals

14 NW Dead Sea -15 km sector Correlation of MD radon signals among three sites Depth: 2 meters Lithology:gravel

15 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. Days since Average annual Rn concentration vs. Earthquakes

17 NW Dead Sea, : Average annual Rn concentration Annual number of earthquakes in the DSF (IJES 2005) Conclusion ( ) Relationship found between: Annual average Rn level and Annual number of EQ along DSR

km 200 km The relation between MD radon signals (at site 17W) & earthquakes along the Dead Sea Transform For ( ) Relationship found between: Annual average Rn level and Annual number of EQ along DSR

19 M>2 M< earthquakes, 4.2 ≥ M L ≥ 0 TECTONIC SEGMENTS Earthquake Catalog Seismological Div., GII

20 (40 Days) minima Smoothing: 25-hour sliding average Start-time of MD radon signal Threshold: 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: M L >=2 RA = Years: No. EQ (M L ≥2) : 165

22 (Steinitz, Begin, Gazit-Yaari, Geology 2003) Timing of 165 earthquakes (M L  2) 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 random occurrence Days after start-time of radon event Dead Sea, Kinneret and Hula pull-apart grabens Number of earthquakes Steinitz et al 2003

23 Previous approach focused on : Counting earthquakes within multi-day Rn anomalies (Steinitz et al., 2003, Geology 31: ) 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 RA EQ Catalog Regional sets MD-starts  EQ queries

25 Rn Start-times

26 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 ( )

28 Definition of “Rn anomaly days” for a time bin of n=3 after 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) YNYN Y N YNYN 1)It is a day in which at least one earthquake (of magnitude ≥M L ) occurred (or not)

30 Are these two attributes independent ? Did at least one earthquake occur in day? Was day within n days after start of Rn anomaly? (One degree of freedom) Yes No Yes No Total number of days Observed Expected Observed Expected Total number of days count EQ (diff) count day-start N total (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 Rn monitor

32 Yes No Total Total number of days Was day within 3 days after start of Rn anomaly? Yes No For earthquakes , M L >0 Out of the Dead Sea rift valley, Rn anomaly cutoff of Rel. Amp: 2.0 Did at least one earthquake occur in day? Total number of days 3094

33 Yes No Total Total number of days Yes No Observed Expected Observed Expected Did at least one earthquake occur in day? Total number of days Was day within 3 days after start of Rn anomaly? For earthquakes , M L >0 Out of the Dead Sea rift valley, Rn anomaly cutoff of Rel. Amp: 2.0

34 Yes No Total Total number of days Yes No Observed Expected Observed Expected [  2 ] = Σ 0.19 Did at least one earthquake occur in day? Total number of days Was day within 3 days after start of Rn anomaly? For earthquakes , M L >0 Out of the Dead Sea rift valley, Rn anomaly cutoff of Rel. Amp: 2.0

35 Yes No Total Total number of days Yes No Observed Expected Observed Expected [  2 ] = Σ 0.19 Did at least one earthquake occur in day? Total number of days Was day within 3 days after start of Rn anomaly? For earthquakes , M L >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 Total Total number of days Yes No Observed Expected Observed Expected [  2 ] = Σ 0.19 Did at least one earthquake occur in day? Total number of days Probability of random occurrence = 0.66 No significant connection Was day within 3 days after start of Rn anomaly? For earthquakes , M L >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 Rn monitor

38 Yes No Total Total number of days Yes No Observed Expected Observed Expected For earthquakes , M L >0 Within the Dead Sea rift valley, Rn anomaly Relative Amplitude > 2.0 Did at least one earthquake occur in day? Total number of days Was day within 3 days after start of Rn anomaly?

39 Yes No Total Total number of days Yes No Observed Expected Observed Expected Did at least one earthquake occur in day? Total number of days Was day within 3 days after start of Rn anomaly? [  2 ] = Σ 7.03 For earthquakes , M L >0 Within the Dead Sea rift valley, Rn anomaly Relative Amplitude > 2.0

40 Yes No Total Total number of days Yes No Observed Expected Observed Expected Did at least one earthquake occur in day? Total number of days Was day within 3 days after start of Rn anomaly? Probability of random occurrence = Significant connection For earthquakes , M L >0 Within the Dead Sea rift valley, Rn anomaly Relative Amplitude > 2.0

41 Analyzing the Rn-EQ connection 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 Total Total number of days Yes No Observed Expected Observed Expected Did at least one earthquake occur in day? Total number of days Was day within 3 days before start of Rn anomaly? [  2 ] = Σ 0.98 For earthquakes , M L >0 Within the Dead Sea rift valley, Rn anomaly Relative Amplitude > 2.0

43 Yes No Total Total number of days Yes No Observed Expected Observed Expected Did at least one earthquake occur in day? Total number of days Was day within 3 days before start of Rn anomaly? Probability of random occurrence = 0.32 No significant connection For earthquakes , M L >0 Within the Dead Sea rift valley, Rn anomaly Relative Amplitude > 2.0

44 M>2 M<2 10 years; Earthquakes, 4.2 ≥ M L ≥ 0 Twelve 4-day time bins around “start” TECTONIC SEGMENTS DSROUT-of- DSR

45 Testing for correlation between Rn MD signals and EQ in DSR Earthquakes: M L ≥0; M L ≥2 10 Years ( ) DSR OUT-of-DSR RA = 1.8; 2.0 bins: 4 days span: -24 to +24 days relative to “start” Observed no. of earthquakes & Expected number Enrichment of earthquakes Testing the statistical significance of enrichment Or Probability that correlation is a random one (using the  2 criterion)

46 Observed - Expected M L >=0 M L >=2

47 Enrichment

48 Statistical significance

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 value of 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 province on an annual basis. 2. This study also presents a significant statistical relationship between Rn anomalies and earthquakes that occur after the start time of the anomalies within the same tectonic province.

53 END Thank You