Seismicity within a zone of plate convergence—the Wellington region, New Zealand

Summary. A telemetered network of sensitive seismographs is being used to study the seismicity of the Wellington region, within the broad shear belt through New Zealand that marks the convergence of the Pacific and Indian plates. On average about 4 event/day are detected within 75 km of the network centre. Of the events located during the first two years of operation, the majority define a band of relatively intense activity, at depths from 20 to 40 km, dipping gently to the north-west and marking some surface near the top of the underthrust Pacific lithosphere. There is less intense and more diffuse activity both above and below this zone. The shallower activity does not correlate with major surface faults and reflects the widespread nature of shallow deformation throughout the shear belt. The mechanism of shallow events well above the band of high activity appears to be a mixture of strike-slip and thrust faulting, while that of at least part of the activity in the band is normal faulting. The rate of activity and b value, as functions of time, show significant variations, some of which may be related to the occurrence of the largest shock of the period, M _L= 6.1.