Went back to the lake to continue study of fractures in ice (see link to previous posts, below). OK, I went to skate but checked out the fractures. It seem that many of the original cracks healed and are not active-in fact, you can't even see them. Some large cracks split open several cm, but these are refrozen and other, newer cracks cut across them. It looks like cracks in this ice heal and are not weaker than the ice around them. This is true also for faults in sandstone. Aydin and Johnson studied this in Utah. I found examples on Santa Rosa Island, California. There are deformations bands a meter or a few meters across with dozens to hundreds of slip surfaces. The faults become stronger than the rock adjacent, so that a new slip surface is formed. Eventually, one surface may become weaker and take off....slipping 100s of m of maybe even a couple km...(at least vertical separation of beds on pure strike-slip faults suggests large slips).
One flat coastal outcrop had 3 faults sets-the oldest was E-W striking, and it was offset by right-lateral N-S faults and by left-lateral NE-SW faults. The NE-SW and N-S faults mutually offset each other (they were/are active at the same time. You can match the faults up across the other faults-the slip was often tens of cm. These may be formed in single earthquakes....but I guess I can't prove it.

In other settings, the same slip surface fails again and again.....
Chris

• previous ice fracture posts