Marine Ecosystems Research Department - jamstec japan agency ...

Japan Marine Science and Technology Center
Institute for Frontier Research on Earth Evolution (IFREE)
2000
Onset: 2001 2 16 15 7 46.025302
1000
P
0
-1000
-2000
-3000
Fig.32 A browsing window of an "Advanced Search" in which one
can use search options of geomagnetic disturbance levels
and data missing rates in addition to data periods and
stations.
-4000
0 2 4 6 8 10 12 14 16
Seconds
Fig.33 Example of automatic picking of first arrival P-wave. The
system detected an arrival of P-wave at the time designated
by 'P'.
forms the data to the requested format, and then provides
them to the request users.
This new service will open to the public soon via a
WEB server (http://www.jamstec.go.jp/pacific/).
We will distribute geomagnetic data observed in the
Pacific region by the Ocean Hemisphere network
Project (OHP) through this system, and plan to add
data from other data centers, including submarine
cable voltage data.
3.2. Automatic phase picking system.
We developed an automatic seismic phase detection
system and started to operate it routinely from
the beginning of . Since that time, all seismic
records registered by the seismic stations of Hi-
Net, which is maintained by National Institute for
Earth Science and Disaster Prevention in Tsukuba
and we receive through the satellite transmission system,
were analyzed every time a large earthquake
occurred. In total, earthquakes were registered
and associated seismic traces analyzed (Fig.). The
automatic phase detection system significantly simplifies
data processing. Typically, about minutes
are sufficient to automatically analyze all associated
information. Although the automatic phase detection
algorithm is incomparably faster than analyses performed
by an operator, it is slightly less precise.
Accumulation of an extensive database of times of
first arrivals will allow us to solve this problem using
statistical methods. Moreover, the accumulated associated
information, such as amplitudes of the waveforms,
gives us the opportunity to study the behavior
of wave propagation related to spatial directivity. For
example, earthquakes of magnitude occurring near
Indonesia can be easily detected by the seismological
network while comparable earthquakes at shorter distances
but different locations (for example Mariana),
are hardly seen on the seismic records. Detailed
analysis of this data gives valuable information about
the seismic signal quality registered by the seismic
stations and, in turn, allows us to improve the quality
of our catalogues.
4. Seismic Data Processing Division
4.1. Construction of geophysical database.
To aid crustal studies at IFREE, the seismic data
processing division has been constructing a geophysical
database. As one of the application studies of the
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