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**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) • 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**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 T0 238-U 226-Ra 222-Rn DL/L = 0 T1 Detector s s DL/L=10-7-10-10 Source Advection**Measurement principles**U-238 radioactive decay series Decay → recoil → Rn emanation Detection a g a Solid Geogas 3.82 days 1620 years**Earthquakes1900-1990**Monitoring sites along Dead Sea Transform**Radon monitoring arrays along the Dead Sea Rift (DSR)**• 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 stationscovering a 20km sector • Precambrian basement rocks of uplifted boundary blocks of DSR**NW Dead Sea**19W – 19E Ramon Arava margin A 17W E1, E2, E3 IUI 23W – 23E 21W Roded BGO**High Rn zone**Monitoring Rn (gamma) sensor Integration time: 15 min 1994-2005 C**E**W u u Rn monitoring at 1.2 meter in gravel u u Dead Sea Graben fill Rn on carrier gas U bearing phosphorite u u**Alpha and gamma co-registration**• Radon! • Geophysical sensitivity - High**Days since 1.1.1992**Multi-year, seasonal (and multi-day [MD]) variation signatures and signals • Radon time series of (gamma radiation) in geogas in gravel at main monitoring site, NW Dead Sea, DSR. • Multi-year decrease (relative to stable background originating from solid gravel) • Seasonal variation • Multi-day variations (MD) - statistically correlated to earthquakes in the Dead Sea Rift (Steinitz et al., 2003; see below).**Seasonal, Multi-day (MD) and Diurnal Radon Signals (DRS)**Concordance & correlation of signals • Sites 12 km apart • Next to the main western boundary fault of DSR**NW Dead Sea -15 km sector**• Correlation of MD radon signals among three sites • Depth: 2 meters • Lithology: gravel**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**Days since 1.1.1992**Average annual Rn concentration vs. Earthquakes Multi-year time series of radon (gamma radiation) in geogas in gravel at main monitoring site, NW Dead Sea, DSR.**NW Dead Sea, 1995-2004:**• Average annual Rn concentration • Annual number of earthquakes in the DSF Conclusion (1994-2004) Relationship found between: Annual average Rn level and Annual number of EQ along DSR (IJES 2005)**400 km**200 km For (1994-2004) Relationship found between: Annual average Rn level and Annual number of EQ along DSR • The relation between • MD radon signals(at site 17W) • & • earthquakes along the Dead Sea Transform**M>2**M<2 Earthquake Catalog Seismological Div., GII TECTONIC SEGMENTS 1994-2002 1075 earthquakes, 4.2≥ ML ≥0**Start-time of MD radon signal**Smoothing: 25-hour sliding average Threshold: Relative amplitude > 1.9 Bin = time window (40 Days) minima Extraction “start” of MD Rn signal, time windows, Earthquakes**Correlation between Rn MD signals and EQ in DSR (Geology**2003) For: ML>=2 RA = 1.9 8 Years: 1995-2002 No. EQ(ML≥2): 165**Steinitz et al 2003**Statistical significance -Probability (%) of random occurrence Earthquakes are clustered in the 0-3 days after the start-time of MD Rn signal Number of earthquakes Dead Sea, Kinneret and Hula pull-apart grabens Days after start-time of radon event 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. (Steinitz, Begin, Gazit-Yaari, Geology 2003)**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)**MD-Starts and EQ correlation**Rn time series at 1-hour resolution Smoothing: 25-hour sliding average Residual time series Smoothed time series EQ Catalog Extraction of MD starts, Amplitude and RA Regional sets MD-starts EQ queries**Rn Start-times for Relative Amplitude > 1.9**Earthquakes 3 days**Flowchart for MD-Starts and EQ correlation**Extraction of significant “starts” (n ~ 150) Number of measurement days(1995-2004) Number of EQ in tectonic segment 3 & 4 -day time window (bin), Relative to “start” All bins Expected number of EQ per:a) (1-day) b) 3 & 4 -day time window (bin) All “starts” Count: number of EQ in time window (EQ in time-bin)n starts Histogram: number of EQ in 3 & 4 -day bin Radon time-series Tectonic segment**Definition of “Rn anomaly days” for a time bin of n=3**after the start time of Rn anomalies**Y N**YN Y N YN A day is characterized by two attributes: 1) It is a day in which at least one earthquake (of magnitude ≥ML) occurred (or not) 2) It is a day which occurred n days after the start time of a Rn anomaly,with a certain Relative Amplitude (or not)**Are these two attributes independent ?**Did at least one earthquake occur in day? Use the 2test to determine the probability of random occurrence Total number of days Yes No (One degree of freedom) Observed count day-start Yes Was day within n days after start of Rn anomaly? Expected Observed No (diff) Expected countEQ (diff) Ntotal Total number of days**Analyzing the Rn-EQ connection**1. For earthquakes out of the Dead Sea rift valley Rn monitor**For earthquakes1994-2004, ML >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 Total number of days Yes No Yes Was day within 3 days after start of Rn anomaly? 342 No 3094 Total number of days 607 2829 3436**For earthquakes1994-2004, ML >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 Total Yes No Observed 57 285 Yes Was day within 3 days after start of Rn anomaly? 342 Expected 60.4 281.6 Observed 550 2544 No 3094 Expected 546.6 2547.4 Total number of days 607 2829 3436**For earthquakes1994-2004, ML >0**Out of the Dead Sea rift valley, Rn anomaly cutoff of Rel. Amp: 2.0 [2]= Σ 0.19 Did at least one earthquake occur in day? * Total number of days Total Yes One degree of freedom No Observed 57 285 Yes Was day within 3 days after start of Rn anomaly? 342 Expected 60.4 281.6 Observed 550 2544 No 3094 Expected 546.6 2547.4 Total number of days 607 2829 3436 * Including the Yates continuity correction**For earthquakes1994-2004, ML >0**Out of the Dead Sea rift valley, Rn anomaly cutoff of Rel. Amp: 2.0 [2]= Σ 0.19 Did at least one earthquake occur in day? Total number of days Total Probability of random occurrence = 0.66 No significant connection Yes No Observed 57 285 Yes Was day within 3 days after start of Rn anomaly? 342 Expected 60.4 281.6 Observed 550 2544 No 3094 Expected 546.6 2547.4 Total number of days 607 2829 3436**Analyzing the Rn-EQ connection**2. For earthquakes within the Dead Sea rift valley Rn monitor**For earthquakes1994-2004, ML >0**Within the Dead Sea rift valley, Rn anomaly Relative Amplitude >2.0 Did at least one earthquake occur in day? Total Total number of days Yes No Observed 66 276 Yes Was day within 3 days after start of Rn anomaly? 342 Expected 49.2 292.8 Observed 428 2666 No 3094 Expected 444.8 2649.2 Total number of days 494 2942 3436**For earthquakes1994-2004, ML >0**Within the Dead Sea rift valley, Rn anomaly Relative Amplitude >2.0 [2]= Σ 7.03 Did at least one earthquake occur in day? Total number of days Total Yes No Observed 66 276 Yes Was day within 3 days after start of Rn anomaly? 342 Expected 49.2 292.8 Observed 428 2666 No 3094 Expected 444.8 2649.2 Total number of days 494 2942 3436**For earthquakes1994-2004, ML >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 Total Probability of random occurrence = 0.008 Significant connection Yes No Observed 66 276 Yes Was day within 3 days after start of Rn anomaly? 342 Expected 49.2 292.8 Observed 428 2666 No 3094 Expected 444.8 2649.2 Total number of days 494 2942 3436**Analyzing the Rn-EQ connection**We now test a Rn-earthquake connection within the Dead Sea rift valley for 3 days before the start time of Rn anomalies Rn monitor**For earthquakes1994-2004, ML >0**Within the Dead Sea rift valley, Rn anomaly Relative Amplitude >2.0 [2]= Σ 0.98 Did at least one earthquake occur in day? Total number of days Total Yes No Observed 55 282 Yes Was day within 3 days before start of Rn anomaly? 337 Expected 48.5 288.5 Observed 439 2660 No 3099 Expected 445.5 2653.5 Total number of days 494 2942 3436**For earthquakes1994-2004, ML >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 Total Probability of random occurrence = 0.32 No significant connection Yes No Observed 55 282 Yes Was day within 3 days before start of Rn anomaly? 337 Expected 48.5 288.5 Observed 439 2660 No 3099 Expected 445.5 2653.5 Total number of days 494 2942 3436**TECTONIC SEGMENTS**OUT-of-DSR DSR M>2 M<2 10 years; 1994-2004 Earthquakes,4.2≥ ML ≥0 Twelve 4-day time bins around “start”**Testing for correlation between Rn MD signals and EQ in DSR**DSR OUT-of-DSR 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) 10 Years (1995-2004) RA = 1.8; 2.0 bins: 4 days span: -24 to +24 days relative to “start” Earthquakes: ML≥0; ML≥2**Observed - Expected**ML >=2 ML >=2 ML >=0 ML >=0**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 ]**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.**Summary of results of 10 years of high-resolution Rn**monitoring: