1. A Simple and Rapid earthquake Detection and Discrimination System for ELARMS or A new conceptual schema for earthquake detection Marco Olivieri 1 & Richard M. Allen 2 1) Istituto Naz. Di Geofisica e Vulcanologia, Roma, Italy 2) SeismoLab, UCBerkeley, Berkeley, CA

2. Aim of the project To develop a new earthquake detection algorithm Objective: To speed-up the detection process To reduce false detections Peculiar attention to EEW systems

3. Traditional approach “Absence of evidence is not evidence of absence” Why?

4. Traditional approach (2) Because traditional phase associators do not know: If the missing station is broken. If not, when the pick for that station will be made available. i.e. Detection bases ONLY on the presence of picks in a certain time-window.

5. Modern seismic networks Status monitor: –active-down station (real-time flow monitors) –good ground motion signal (real-time PSD) Latency monitor: –delay in data trasmission These can be updated in real-time

6. A new concept Assumption: If the network is reliable, all the operating stations in the surrounding of the epicenter will detect ground motion change and the picker will produce a P-wave detections with a a priori known delay If the network is reliable, we can look only at close stations

7. Subnets We define the concept of subnet: A subnet is small network made by a master station + the five closest surrounding stations. (If the azimuthal coverage is not appropriate (> 180 o ) we replace some of the stations to enhance it) An earthquake is detected at a subnet when more than 3 stations produce a pick consistent with an hypocenter beneath the master station Or: for each earthquake we will have only one subnet centered above its epicenter

8. MGR subnet (left) AOI subnet (right) this is the case of a “border” subnet (azimuthal gap > 200 o )‏ Each station belong to “its” subnet plus some of the surrounding ones Subnet examples

9. Subnet update schema

10. MTTG subnet Stationlatlondistance azimuthlatency MTTG38.0015.700.14 MSCL38.2315.7927.0621.4813 MPAZ37.9516.0134.1999.2619 CEL38.2615.8935.4437.0315 MSRU38.2615.5035.60323.713 SOI38.0716.0539.7378.8011 Expected relative arrival time for substation: MSCL 3.73 MPAZ 5.110 CEL 5.26 MSRU 5.2 4 SOI 5.8 3 Side effect: The fourth pick is expected 6 +14 seconds= 20. This means that for a EEW we know that an alert can not be earlier than 20 seconds after the eq occurrence, i.e. the area that can not be protected has a radius of about 70km

12. MTTG subnet TIME20080606213905 -1 TIME20080606213906 -1 TIME20080606213907 -1 TIME20080606213908 -1 MTTG2008060621390920080606213855.730 TIME 20080606213909 -1 MSRU 20080606213910 20080606213900.840 TIME 20080606213910 -1 CEL 20080606213911 20080606213900.820 MSCL 20080606213911 20080606213859.430 SOI 20080606213911 20080606213901.300 TIME 20080606213911 -1 TIME 20080606213912 -1 TIME 20080606213913 -1 TIME 20080606213914 -1 TIME 20080606213915 -1 TIME 20080606213916 -1 MPAZ 2008060621391720080606213857.020 Master matching pick MPAZ subnet Data Flow Substation matching pick Step 1

13. MTTG subnet TIME20080606213905 -1 TIME20080606213906 -1 TIME20080606213907 -1 TIME20080606213908 -1 MTTG2008060621390920080606213855.730 TIME 20080606213909 -1 MSRU 20080606213910 20080606213857.840 TIME 20080606213910 -1 CEL 20080606213911 20080606213855.820 MSCL 20080606213911 20080606213855.030 SOI 20080606213911 20080606213856.300 TIME 20080606213911 -1 TIME 20080606213912 -1 TIME 20080606213913 -1 TIME 20080606213914 -1 TIME 20080606213915 -1 TIME 20080606213916 -1 MPAZ 2008060621391720080606213857.020 2 picks MPAZ subnet Data Flow 1 pick Step 2, 2 seconds later TIME20080606213905 -1 TIME20080606213906 -1 TIME20080606213907 -1 TIME20080606213908 -1 MTTG2008060621390920080606213855.730 TIME 20080606213909 -1 MSRU 20080606213910 20080606213900.840 TIME 20080606213910 -1 CEL 20080606213911 20080606213900.820 MSCL 20080606213911 20080606213859.430 SOI 20080606213911 20080606213901.300 TIME 20080606213911 -1 TIME 20080606213912 -1 TIME 20080606213913 -1 TIME 20080606213914 -1 TIME 20080606213915 -1 TIME 20080606213916 -1 MPAZ 2008060621391720080606213857.020 TIME20080606213905 -1 TIME20080606213906 -1 TIME20080606213907 -1 TIME20080606213908 -1 MTTG2008060621390920080606213855.730 TIME 20080606213909 -1 MSRU 20080606213910 20080606213900.840 TIME 20080606213910 -1 CEL 20080606213911 20080606213900.820 MSCL 20080606213911 20080606213859.430 SOI 20080606213911 20080606213901.300 TIME 20080606213911 -1 TIME 20080606213912 -1 TIME 20080606213913 -1 TIME 20080606213914 -1 TIME 20080606213915 -1 TIME 20080606213916 -1 MPAZ 2008060621391720080606213857.020

14. MTTG subnet TIME20080606213905 -1 TIME20080606213906 -1 TIME20080606213907 -1 TIME20080606213908 -1 MTTG2008060621390920080606213855.730 TIME 20080606213909 -1 MSRU 20080606213910 20080606213857.840 TIME 20080606213910 -1 CEL 20080606213911 20080606213855.820 MSCL 20080606213911 20080606213855.030 SOI 20080606213911 20080606213856.300 TIME 20080606213911 -1 TIME 20080606213912 -1 TIME 20080606213913 -1 TIME 20080606213914 -1 TIME 20080606213915 -1 TIME 20080606213916 -1 MPAZ 2008060621391720080606213857.020 5 picks: event detected MPAZ subnet Data Flow 3 picks not matching: Event killed Step 3, 4 seconds later TIME20080606213905 -1 TIME20080606213906 -1 TIME20080606213907 -1 TIME20080606213908 -1 MTTG2008060621390920080606213855.730 TIME 20080606213909 -1 MSRU 20080606213910 20080606213900.840 TIME 20080606213910 -1 CEL 20080606213911 20080606213900.820 MSCL 20080606213911 20080606213859.430 SOI 20080606213911 20080606213901.300 TIME 20080606213911 -1 TIME 20080606213912 -1 TIME 20080606213913 -1 TIME 20080606213914 -1 TIME 20080606213915 -1 TIME 20080606213916 -1 MPAZ 2008060621391720080606213857.020

16. Conclusions enhance the rapid detection capability for a dense network of seismic stations in terms of: –Delay for the event declaration –False alert generated by sparse picks give a real-time and punctual information for the detection delay of the forthcoming earthquake (a crucial input for EEW systems) the work is absolutely in progress

17. Association Diagram

18. example TIME 20080606213901 -1 TIME 20080606213902 -1 TIME 20080606213903 -1 TIME 20080606213904 -1 TIME 20080606213905 -1 TIME 20080606213906 -1 TIME 20080606213907 -1 TIME 20080606213908 -1 MTTG 20080606213909 20080606213855.730 TIME 20080606213909 -1 MSRU 20080606213910 20080606213857.840 TIME 20080606213910 -1 CEL 20080606213911 20080606213855.820 MSCL 20080606213911 20080606213855.030 SOI 20080606213911 20080606213856.300 TIME 20080606213911 -1 TIME 20080606213912 -1 TIME 20080606213913 -1 TIME 20080606213914 -1 TIME 20080606213915 -1 TIME 20080606213916 -1 MPAZ 20080606213917 20080606213857.020 Latency issue: If latency is not constant over the different stations (and usually it is not!) the first incoming trigger can belong to a station that is not closest one to the epicenter