A DETAILED STUDY OF TELESEISMIC P-WAVE TRAVEL TIME RESIDUALS AT AHMADU BELLO UNIVERSITY ZARIA SEISMIC STATION

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dc.contributor.authorONIKU, ADETOLA SUNDAY
dc.date.accessioned2014-02-06T08:58:41Z
dc.date.available2014-02-06T08:58:41Z
dc.date.issued1999-08
dc.descriptionA RESEARCH WORK SUBMITTED TO THE DEPARTMENT OF PHYSICS AHMADU BELLO UNIVERSITY, ZARIA IN PARTIAL FULFILLMENT FOR THE AWARD OF M. Sc. DEGREE IN APPLIED GEOPHYSICSen_US
dc.description.abstractThe teleseismic P-wave travel time residuals at the Ahmadu Bello University (A.B.U.) Zaria seismic station were measured with respect to the Jeffery-Bullen (JB) tables. A total of two hundred and thirty (230) events at epicentral distances between 24° and 180° was selected from recordings covering the period January 1985 to December, 1992. The limited number of events used was due to the low operational gain (due to high cultural background noise) at the station which permitted only events whose magnitudes are large enough to be picked. This was further reduced to 108 events which have residuals less or equal to 5. The data obtained were used to create the station history plots which display the travel-times on the distance-time curve, event locations on a world map centered at Zaria and the P-wave residuals for the station. The station absolute residuals for all the selected events vary between -4.1 s to 5.0 s with an average value of 1.08 s ± 2.0 s. The azimuthal biases were then taken into consideration by sorting the residuals into 10° azimuth by 10° distance bins. A new station average residual was calculated to be 0.72 ± 1.81 s by summing over the average residual for that bin. These are then referred to as the residuals before and after sorting respectively. The large standard deviation of the average residuals suggests that the variation in the residuals cannot be accounted for by considering the data as belonging to one homogeneous set. The data set was therefore sub-divided into five regions on the basis of similar azimuths and propagation path to the station. The average residuals for each of the five regions are: (i) Mediterranian +1.05±0.85s (ii) Kazakhstan -0.90+0.40 s (iii) Burma/lndia/China +2.33+1.18 s (iv) South and Central America +1.40+1.00 s (v) North Ascension Island +0.20+0.70 s Relative travel time residuals of the station were calculated with reference to some group of stations located in the stable West-African Craton, Congo Craton and the seismically active East-African rift valley by considering some events distributed randomly in the five different regions. It was found that the trend of the relative residuals is an indication of lateral inhomogeneity of the crust and upper mantle between the various stations and Zaria station. It was also found that the relative residuals are highly dependent on the direction of approach of the P-waves. An inversion of the travel time data was attempted using the tau-p method of inversion. However the observed data were found to be too few and sparse in any given azimuth to yield meaningful results.en_US
dc.identifier.urihttp://hdl.handle.net/123456789/361
dc.language.isoenen_US
dc.subjectDetailed,en_US
dc.subjectSTUDY,en_US
dc.subjectTELESEISMIC,en_US
dc.subjectP-WAVE,en_US
dc.subjectTRAVEL,en_US
dc.subjectTIME,en_US
dc.subjectRESIDUALS,en_US
dc.subjectAHMADU BELLO UNIVERSITY ZARIA,en_US
dc.subjectSEISMIC,en_US
dc.subjectSTATIONen_US
dc.titleA DETAILED STUDY OF TELESEISMIC P-WAVE TRAVEL TIME RESIDUALS AT AHMADU BELLO UNIVERSITY ZARIA SEISMIC STATIONen_US
dc.typeThesisen_US
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