Identify the true statement. a. Local magnitude (ML) rating is the number now used for the official (archival) record. b. All earthquake magnitude scales are logarithmic, which means that a difference of one unit in magnitude reading represents a 10-fold difference in ground motion. c. The ML earthquake magnitude scale (Richter) can accurately define extremely large earthquakes. d. Thrust faults result from stretching the Earth's crust; normal faults, from squeezing and shortening it.