Sentence:  It has been noted, using a combination of surface geologic and seismic reflection data, that a <WSD>duplex</WSD>, although formed in response to movement of a thrust sheet, frequently arches the thrust sheet as the duplex is built by duplication of rocks beneath it ... 
Meaning of the word marked with <WSD> tags:  A system of multiple thrust faults bounded above and below by a roof thrust and floor thrust.