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  جداول بيانات الأحداث الزلزالية

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 GENERAL BULLETIN INFORMATION

 

GENERAL BULLETIN INFORMATION
The Yemen National Seismic Network consist of the stations listed below which are operated by ( NSOC ) National Seismological Observatory Center    (Geological Survey and Mineral Resources Board, Ministry of Oil and Minerals ) .
Station     Latitude        Longitude Height (m) SANA  15.387N  44.205E  2280 DHBB  14.571N  44.390E  2460 ADEN  12.776N  44.983E  41 BDHA  13.975N  45.567E  2000 HAJJ  15.699N  43.599E  1650 MARB  15.464N  43.992E  1120 UDYN  13.967N  43.967E  1370 TRBA  13.231N  44.115E  1860 SADA  16.933N  43.750E  1850 LBOS  13.871N  45.249E  2325 MUKL  14.476N  49.036E  41 RADA  14.439N  44.853E  2353 ERIN  14.230N  44.230E  1600 SMRH  14.184N  44.257E  2990 ADDN  14.353N  43.850E  2598      The location program currently used for locating earthquakes is HYPOCENTER   ( Lienert et all, 1986 ). For locating local and regional seismic events layered model were assumed, while for locating distant earthquakes IASPEI travel time tables were used. The layered model used for local and regional seismic events is published by  Egolff  et al.,  1990 .
Depth of the layer (Km)	P-wave Velocity ( Km/Sec)
-2	3.4
0.5	4.2
2	6
12.5	6.2
27	6.8
28	7
58	8
The Vp/Vs ratio used in the layered model is 1.73.                Local magnitude ML is determined from maximum amplitude of the ground displacement of the seismic traces after making the proper  corrections for the instrument type to simulate the output of the standardized Wood Anderson instrument. ML is calculated using XPITSA software for seismic analysis ( Scherbaum, F., and Johnson, J., 1992).
The body wave magnitude Mb is calculated using the HYPOCENTER built in formula (Lienert R., 1994):
Mb = log10  + Q( D, d)
where A is the instrument corrected P-wave amplitude (nm) , T  is the period ( sec ), and Q( D, d) is a distance - depth correction factor.
No fixed depth or epicenter location used during the data analysis. Location of some events might be unrealistic such as zero depth earthquakes this is because of the limitation of the available data and reflect the location procedure and the velocity - depth model used.      *Notice : There are Two Temprory stations ( HIMA and BRBR ) operated for short period of time to monitor after shock activity. On the other hand the location of TRBA station was slightly changed starting from the beginning of 2004 due to noise problem in the old location.
Abbreviations:
Month      : month of the year
Day          : day of month
Station     : station code
Phase     : phase, The first characterizes onset E ( Emergent ) or I ( Impulsive ) and polarity U
for Compress ional ) or D ( for Dilatation ). For the located events calculated phase is given.
Arr. Time: first arrival of the wave to the station ( hh mm sec ).
Mag       : Local magnitude.
Origin Time: the origin time of the located event ( yymmdd   hhmm   sec).
Location : epicenter location of the event ( Latitude degree north , Longitude degree south )
Depth     :  the focal depth in kilometers.
ML      : Local Magnitude.
Mb      : Body Wave Magnitude.
Mc          : Coda Magnitude.