Discovery of Strike-Slip Faulting In the Alps

The first faults ever to be noticed were normal faults in mines. However, soon other kinds of faults were also noticed, but all such faults had small enough throws to enable the miner to find the offset seam or the ore within his mine. Large offset faults were recognised when geological mapping became a wiedspread practice in the nineteenth century. Initally only two kinds were noticed: normal and thrust faults. When Arnold Escher von der Linth began mapping in the Säntis mountains of northeastern Switzerland he noticed near Rasenäuli a major fault of essentially vertical dip that had horizontal striations on its slickensides. He was much puzzled by this obesrvation and showed it to Eduard Suess in 1854 who visited him. Suess in his ‘Face of the Earth' gives the entire credit of discovering strike-slip faults on a large scale to Escher. However, when Escher's field note-books are examined there is not a word of interpretation and neither is there any statement of strike-slip faulting in the posthumously published version of the Säntis monograph. We know that his editor Casimir Moesch altered Escher's map to make the fault into a horizontal flexure, for which he was later chastised by Albert Heim. However, Suess later much used the concept of strike-slip faulting (called Blatt, i.e., leaf, plural Blätter, by Alpine miners) in his mapping and interpretations of the Alps and in 1909 ascribed some of the young Cordilleran basins, such as the Death Valley, to strike-slip faulting. In fact strike-slip fault interpretations became inevitable when the large amounts of horizontal motion was discovered in the Alps. It was in the Alps that strike-slip faults first became an integral part of terrestrial tectonics through Suess' work, from where it went into Alfred Wegener's writings.