ausblenden:
Schlagwörter:
Mantle processes; Seismic tomography; Oceanic hotspots and intraplate volcanism
Zusammenfassung:
We present results of a non-linear teleseismic P-wave traveltime tomography in Ireland. Relative traveltime residuals are calculated from the data set of the Irish Seismological Lithospheric Experiment (ISLE 2002/3) and permanent stations onshore Ireland. At each of the 28 station sites, a local crustal 1-D P-wave velocity (vP) model is determined because the 3-D crustal vP structure of Ireland is well known. These 1-D models are used for a traveltime correction for crustal effects. The corrected residuals indicate two large-scale traveltime anomalies of low amplitude: a negative traveltime anomaly in the western part of Ireland and a positive anomaly in the eastern part of the country. The subsequent traveltime tomography is calculated using an iterative non-linear inversion using a variable parametrization and 3-D ray tracing. Our inversion result contains a low P-wave velocity (vP) zone underneath central Ireland, at 31–120 km depth. The amplitudes of the low velocity zone reach up to −2.5 per cent vP at 31–60 km depth, but decrease to −0.5 to −1 per cent vP at 120–150 km depth. Reconstruction tests confirm that large anomalies in our model are well resolved, although the resolution decreases towards the edges of the model. We infer that the low velocity zone underneath central Ireland is related to lithospheric thinning towards the north, which was determined by a previous S-receiver function study. This anomaly is interpreted as presumably ancient or even recent mantle upwelling, related to the spreading of the Iceland plume head.
