A Simple and Rapid earthquake
Detection and Discrimination
System for ELARMS
or
A new conceptual schema for earthquake
detection
Marco Olivieri1 & Richard M. Allen2
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 (> 180o)
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
Subnet examples
• MGR subnet (left)
• AOI subnet (right) this is the case of a
“border” subnet (azimuthal gap > 200o)
• Each station belong to “its” subnet plus some of the
surrounding ones
Subnet update schema
MTTG subnet
Station
MTTG
MSCL
MPAZ
CEL
MSRU
SOI
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
lat
38.00
38.23
37.95
38.26
38.26
38.07
lon
15.70
15.79
16.01
15.89
15.50
16.05
distance
0.
27.06
34.19
35.44
35.60
39.73
azimuth
21.48
99.26
37.03
323.7
78.80
Expected relative arrival time for
substation:
MSCL
3.7
3
MPAZ
5.1
10
CEL
5.2
6
MSRU
5.2
4
SOI
5.8
3
latency
14
13
19
15
13
11
MPAZ subnet
Data Flow
TIME
20080606213905
TIME
20080606213906
TIME
20080606213907
TIME
20080606213908
MTTG
20080606213909
TIME 20080606213909
-1
MSRU
20080606213910
TIME 20080606213910
-1
CEL
20080606213911
MSCL
20080606213911
SOI
20080606213911
TIME 20080606213911
-1
TIME 20080606213912
-1
TIME 20080606213913
-1
TIME 20080606213914
-1
TIME 20080606213915
-1
TIME 20080606213916
-1
MPAZ
20080606213917
Substation matching pick
-1
-1
-1
-1
20080606213855.730
MTTG subnet
20080606213900.840
20080606213900.820
20080606213859.430
20080606213901.300
20080606213857.020
Master matching pick
Step 1
Data Flow
MPAZ subnet
TIME
20080606213905
TIME
20080606213906
TIME
20080606213907
TIME
20080606213908
MTTG
20080606213909
TIME 20080606213909
-1
MSRU
20080606213910
TIME 20080606213910
-1
CEL
20080606213911
MSCL
20080606213911
SOI
20080606213911
TIME 20080606213911
-1
TIME 20080606213912
-1
TIME 20080606213913
-1
TIME 20080606213914
-1
TIME 20080606213915
-1
TIME 20080606213916
-1
MPAZ
20080606213917
-1
-1
-1
-1
20080606213855.730
MTTG subnet
20080606213857.840
20080606213900.840
20080606213855.820
20080606213900.820
20080606213855.030
20080606213859.430
20080606213856.300
20080606213901.300
20080606213857.020
2 picks
1 pick
Step 2, 2 seconds later
MPAZ subnet
Data Flow
TIME
20080606213905
TIME
20080606213906
TIME
20080606213907
TIME
20080606213908
MTTG
20080606213909
TIME 20080606213909
-1
MSRU
20080606213910
TIME 20080606213910
-1
CEL
20080606213911
MSCL
20080606213911
SOI
20080606213911
TIME 20080606213911
-1
TIME 20080606213912
-1
TIME 20080606213913
-1
TIME 20080606213914
-1
TIME 20080606213915
-1
TIME 20080606213916
-1
MPAZ
20080606213917
3 picks not matching:
Event killed
-1
-1
-1
-1
20080606213855.730
MTTG subnet
20080606213857.840
20080606213900.840
20080606213900.820
20080606213855.820
20080606213855.030
20080606213859.430
20080606213856.300
20080606213901.300
20080606213857.020
5 picks: event detected
Step 3, 4 seconds later
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 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