Complex sentence: In addition, two 6.0 M w aftershocks occurred about 1 minute after the initial event, and again 11 hours later, the strongest of several thousand aftershocks in all.
Split into simpler sentences: In addition, two 6.0 M w aftershocks occurred. The first about 1 minute after the initial event and the second approximately 11 hours later, the strongest of several thousand aftershocks in all.