THE SECOND LARGE EARTHQUAKE OCCURRING THREE DAYS LATER

The IMO determined origin time of the June 21 earthquake was 00:51:46.95 GMT, the hypocenter was at 63.98$^{\circ}$N, 20.71$^{\circ}$W, and a hypocentral depth of 5.1 km. The aftershocks indicate a vertical fault, 15 km long, striking N2$^{\circ}$W extending from the surface to 8 km depth (Figure 3).

 

Figure 3: The figure shows the aftershocks of the June 21 earthquake, within 3 km of the fault plane. The frame at the top shows aftershocks during the first 32 hours. The second frame shows the aftershocks until December 10, 2000.

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Surface fissures indicating general right-lateral motion (Einarsson et al. 2000) coincide with and are found all along the main fault as it is reflected in the aftershocks. Related ENE-WSW fault with left-lateral motion was also observed near the southern end of the main fault. The USGS Rapid Moment Tensor Solution gives a moment of $5.2\ast10^{18}$ Nm, assuming a best fitting double-couple solution. Preliminary magnitudes by NEIC were mb=6.1 and Ms=6.6. The strainmeter observations were not good enough to provide an independent estimate of the moment. Assuming uniform right-lateral slip as indicated by the surface fissures, fault size indicated by the aftershocks and the moment of USGS, a 1.2 meter right-lateral coverage slip of the main fault is implied.