Greinar (Vísindafélag Íslendinga) - 01.01.1976, Page 51

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able. To avoid errors caused by statíon residuals and lateral inho-
mogeneitíes along the rays it is important to use always the same
station set for the locations.
To assure a consistent picking of the P-wave arrival the wave
trains of all events as recorded at one station were correlated visu-
ally with the P-wave train of the master event. A corresponding
arrival was then picked for all events. This procedure was found
to improve significantly the quality of the locations. Inherent in
this method are the assumptions that all events occurred at approxi-
mately the same depth and had similar focal mechanism. Earth-
quakes on the Reykjanes Peninsula in SW Iceland occur mostly
at depths of 2-5 km (10) and earthquakes in the Tjömes Fracture
Zone can be expected to occur at similar depths. The assumption
of similar focal mechanism hmits the applicability of this method.
It is, for example, not safe at the present time to locate the earth-
quake sequence of October 1973 with respect to the sequences of
1969, since a similar tectonic origin is not certain. In this paper
earthquakes of 1968 and 1969 are studied. Of these earthquakes
(No. 21-31 in Table 1) only one (No. 30) was too small for this
analysis.
The seismic stations used in this study were AKU, KTG, UME,
NUR, BMO and UBO. All seismographs from the first four stations
were read by the author but for the last two stations readings were
taken from the EDR bulletin. The station AKU in Iceland (Figure
2) was used as a reference station and for a particular earthquake
the arrival time at AKU was subtracted from the arrival times at
the other stations. These travel time differences were then com-
pared to the corresponding travel time differences for the master
earthquake.
We consider two stations, A and B. At these stations the travel
times, tA and tB of the earthquake to be located can be expressed as
tMA and tMB are the travel times for the master event to the sta-
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