D20 Catalog of relocated earthquakes, fault planes, and subsurface faults – IMO+NVI

This deliverable has not been completed and is delayed to M42. However, significant progress has been made towards completing the catalog.

The data set was divided into pre-1997 and 1997-1999, when logging of time accuracies in wave forms became standard in the wave-form headers. The Hengill area is divided into six overlapping boxes and events in each box analyzed separately. Over 20 thousand events from Jan 1997 to December 1999 have already been relatively located and determination of fault planes and slip directions made. The figure below shows the main findings for the period 1997-1999. Events from the NE sector have not yet been analyzed for years 1997 and 1998.

The ~N-S direction dominant in the South Iceland Seismic Zone (SISZ) is clear in the aftershocks of the M5 and two M>4.5 events from June 4 1998, when rupture propagated from north to south, through the width of the SISZ (~64.07N - ~63.95N). Fault directions at the northern margin of the SISZ, in the area around the center of uplift, on the other hand, are a combination of E-W and NE-SW. At the southern margin of the SISZ, the main fault, associated with the M5 event of November 13 1998, is directed ENE-WSW, and off-set in the center by the N-S directed SISZ fault. The M>4.5 event from November 14, 1998 is on a NW fault mapped by the aftershocks.

Relatively located events (open purple circles) from 1997 through 1999, and faults already analyzed (open black circles). Events greater than M4.5 are displayed with stars and mechanisms for the two M5 events are shown. Previously mapped surface faults are shown with thin black lines. The arching yellow line indicates the mapped fault scarp following the June 1998 earthquake swarm. The center of uplift is indicated by a solid black circle. Seismic stations (kro and bja) are shown as purple triangles.