National Seismological Networks By Nageeb AbdulgalilA'Razzaq G'D' of Seismological Networks Seismolo

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National Seismological Networks
By
Nageeb AbdulgalilA.Razzaq G.D. of
Seismological Networks Seismological
Observatory Center Republic of
YemenSymposium on Earthquake and Tsunami
Disaster Preparedness and Mitigation 7-10
NOVEMBER, 2006 BANGKOK, TAILAND.
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National Seismological Networks 1-Digital
Network -Installation was achieved at
the end of November 1994.- -12 of
these stations are equipped with Short Period
(SP) seismometers .
-the other six are Broad Band (BB) seismometer.
2-Analog Telemetry
Network. This network composed of three
stations equipped with Kinematics
SS- 1 short period vertical
component seismometers had been
installed in 1997 around Dhamar
3-Strong Motion Network. Installed
by the mid of 1993, consisting of eighteen SSA-2
based stations distributed in various
parts of Yemen.
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Each short period station consist of a Lennartz
LE-3D tri-axial seismometer, with natural
frequency 1 Hz, Mars-88/MC seismograph, GPS
timing system, modem and a 12 V battery that is
recharged by solar panel on all of the stations.
The Broad Band stations equipped with Gurlap
CMG-40 T seismometer.
Remote Station composed of Mars-88/MC
seismograph-GPS-Solar panel Dry battery)
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The central station is locating in Dhamar and
equipped with three workstations(2HP workstations
and SUN workstation) and two Gateways running
Unix operating system.
Sun workstation( Central station in
Dhamar)



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Seismic Data analysis At the central station,
digital data and analog registers (seismograms)
are processed. When an event needs to be
localized, one of the first steps is to identify
if it is local, regional or teleseismic. All
earthquakes localized within the territory of
Yemen latitudes 13º N-17º N and longitudes 42º
E-56º E are considered local. The XPITSA program
and SEISAN software package are being used for
seismic data processing and HYPOCENTER program
used to locate seismic events using local
velocity model. Magnitudes are calculated by
using the maximum amplitude and registered
duration times (CODA) that each station
registers, using the XPITSA and HPOCENTER
programs built in formulas to determine the event
location, P and S wave arrival times, wave
polarity and lecture qualities are required. To
determine the magnitude it is necessary to read
the duration (CODA) and the maximum amplitude of
the waveforms registered by each station that
detected the event.
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Analog Telemetry NetworkThis network composed
of three stations equipped with Kinemetrics SS-1
short period vertical component seismometers had
been installed in 1997 around Dhamar City at a
vertex of a triangle.
Telemetry Network
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Strong motion station (SSA-2)
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?Epicenteral Distribution Map 2004
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Conclusion and recommendations Since the
installation of the Yemen Digital Seismological
National network at the end of November 1994, it
proved its efficiency and sensitivity to record
local and distant earthquakes. Many distant
earthquakes with big magnitudes can be cached and
determine its location and magnitude using XPITSA
and SEISAN software package. STA / LTA algorithm
is used to Trigger events which stored in the
remote station memory. The data is collected in
near real time using telephone line from the
remote stations. We believe that Yemen digital
seismological network is very benefit for data
exchange and can be used as warning system for
earthquakes and tsunami needing of some support
to develop of the system for real time recording
by change the system from Triggering to satellite
system Digital network in Yemen proved its
efficiency for data exchange and NSOC became
member in EMSC ISC. Adding some very Broad
Band stations in some areas in Yemen and connect
them to the network is recommended.
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Thank you For Listening