Characteristics of the May 12,2008 Wenchuan M_S8.0 Earthquake Sequence and Discussion on Relevant Problems

The aftershock activity of the May 12, 2008 Wenchuan Ms8.0 Earthquake Sequence shows an obvious segmented feature. Most of the large aftershocks were distributed in the north and south parts of the aftershock zone. Thrusting was dominant with a small amount of strike-slip component in the south part. The aftershock activity decayed gradually, presenting the sequence features of a mainshock-aftershock pattern. The north part was the ending area of the malnshock fracture where strike-slipping was dominant, showing an obvious swarm feature. Therefore it became the major area for large aftershocks. The modulation of the earth tide on aftershock activity is remarkable; most large aftershocks occur during the period of flood and neap tide. The time period around 16：00 was the dominant occurring time for large aftershocks. The p-value, a parameter of modified Omori formula, increases gradually with time, and reaches about 1 at the end. Based on previous study, the sequence patterns, magnitude of maximum aftershock, as well as the duration of aftershock activity has been discussed. The primary results also show that the magnitude difference between the maiushock and the maximum aftershock is proportional to the rupture size of the maiushock for huge earthquakes of about Ms8.0. This means that when the magnitudes of the earthquakes are nearly the same, large rupture size corresponds to sufficient energy release.

The aftershock activity of the May 12,2008 Wenchuan M_S8.0 Earthquake Sequence shows an obvious segmented feature.Most of the large aftershocks were distributed in the north and south parts of the aftershock zone.Thrusting was dominant with a small amount of strike-slip component in the south part.The aftershock activity decayed gradually,presenting the sequence features of a mainshock-aftershock pattern.The north part was the ending area of the mainshock fracture where strike-slipping was dominant,showing an obvious swarm feature.Therefore it became the major area for large aftershocks.The modulation of the earth tide on aftershock activity is remarkable;most large aftershocks occur during the period of flood and neap tide.The time period around 16:00 was the dominant occurring time for large aftershocks.The p-value,a parameter of modified Omori formula,increases gradually with time,and reaches about 1 at the end.Based on previous study,the sequence patterns,magnitude of maximum aftershock,as well as the duration of aftershock activity has been discussed.The primary results also show that the magnitude difference between the mainshock and the maximum aftershock is proportional to the rupture size of the mainshock for huge earthquakes of about M_S8.0.This means that when the magnitudes of the earthquakes are nearly the same,large rupture size corresponds to sufficient energy release.