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

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

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

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.

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

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

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

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

Subnet update schema

MTTG subnet Stationlatlondistance azimuthlatency MTTG MSCL MPAZ CEL MSRU SOI Expected relative arrival time for substation: MSCL 3.73 MPAZ CEL 5.26 MSRU SOI Side effect: The fourth pick is expected 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

MTTG subnet TIME TIME TIME TIME MTTG TIME MSRU TIME CEL MSCL SOI TIME TIME TIME TIME TIME TIME MPAZ Master matching pick MPAZ subnet Data Flow Substation matching pick Step 1

MTTG subnet TIME TIME TIME TIME MTTG TIME MSRU TIME CEL MSCL SOI TIME TIME TIME TIME TIME TIME MPAZ picks MPAZ subnet Data Flow 1 pick Step 2, 2 seconds later TIME TIME TIME TIME MTTG TIME MSRU TIME CEL MSCL SOI TIME TIME TIME TIME TIME TIME MPAZ TIME TIME TIME TIME MTTG TIME MSRU TIME CEL MSCL SOI TIME TIME TIME TIME TIME TIME MPAZ

MTTG subnet TIME TIME TIME TIME MTTG TIME MSRU TIME CEL MSCL SOI TIME TIME TIME TIME TIME TIME MPAZ picks: event detected MPAZ subnet Data Flow 3 picks not matching: Event killed Step 3, 4 seconds later TIME TIME TIME TIME MTTG TIME MSRU TIME CEL MSCL SOI TIME TIME TIME TIME TIME TIME MPAZ

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

Association Diagram

example TIME TIME TIME TIME TIME TIME TIME TIME MTTG TIME MSRU TIME CEL MSCL SOI TIME TIME TIME TIME TIME TIME MPAZ 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