Thrust Faulting

Thrust Faulting -- YEC Claims versus Reality

Creationists frequently claim that there are "many places" where supposedly older strata are found above supposedly younger strata. This is offered as "proof" that the geologic column is a "myth." However, if you go and look at creationist webpages making this claim, you will find that they are simply talking about nappes and thrust faults, for instance the Lewis Thrust.

This claim was popularized by Henry Morris, who apparently took the claim from George Price. Morrisdiscussed the Lewis Thrust as an example of "out-of-order" strata, and his comments are still widely quoted on YEC webpages with regard to thrust faulting. He mentions thrust faulting on small scales, but dismisses the whole idea of large thrust faults, proclaiming:

"It seems almost fantastic to conceive of such huge areas and masses of rock really behaving in such a fashion, unless we are ready to accept catastrophism of an intensity that makes the Noachian Deluge seem quiescent by comparison! Certainly the principle of uniformity is inadequate to account for them. Nothing we know of present earth movements, of rock compressive and shearing strengths, of the plastic flow of rock materials, or of other modern physical processes, gives any observational basis for believing that such things are happening now or ever could have happened, except under extremely unusual conditions." (The Genesis Flood, p. 180-181)

Now, like so many other bold geologic claims in Morris' book, this one has not withstood the test of time, and Morris will now have to eat his words. Thrust faulting is not impossible. It does not require a catastrophe in Morris' sense. In fact, mountain-building and large scale thrust faulting are demonstrably occurring in several places in the world today.

Let's use Taiwan as an example. Taiwan is cut by several large-scale thrust faults. Movement along these thrusts occur as a result of tectonic compression between the Phillipine plate and the Eurasian plate, at a rate of about 81mm/yr (Yu S.B., Chen H.Y., and Kuo L.C., 1997, Velocity field of GPS stations in the Taiwan area, Tectonophysics, 274 : 41-59). The Central Mountains in Taiwan are still rising as a result, at a rate of about 5-7mm per year. These mountains are very young, only about 4my old or less. Strata exposed in the foothills of the mountains are Miocene and younger, supposedly "post-flood" sediments.

Below is an east-west cross section through the island of Taiwan, showing several active thrust faults:

You can find more info on the tectonic structure of Taiwan at the links below:

http://www.iris.washington.edu/taiwan/chi-chi4.html

http://www.geo.uu.nl/~bos/taiwan.html

"The island of Taiwan is located in a tectonically complex region where the Ryukyu and Manila Trenches meet at the northwestern corner of the Philippine Sea Plate. The northwestern movement of the Philippine Sea Plate at a rate of 8.2 cm/year creates the Taiwan collision zone which is made up of a series of subparallel thrust faults that run in north and northeast directions in Taiwan. These active thrust faults produce numerous moderate to large earthquakes, with about five M7 earthquakes a century on this relatively small island (330 x 120 km2). Significant events this century include 1906 Chiayi (M7.1), 1935 Hsinchu-Taichung (M7.1), 1941 Chiayi (M7.1), 1964 Baiho (M6.5), and the Chichi earthquake (M7.7) of September 21, 1999."

To give one specific example of observed thrust motion along these thrust faults, the M7.7 1999 Chi Chi earthquake produced over 60 km of surface faulting, and lateral displacements up to 9 meters along the low-angle Chelungpu thrust fault. Along this fault, Pliocene to Pleistocene shallow marine sediments were thrust westward over more recent alluvium, thus creating a "wrong order."

"Early on the morning (01:47 local time) of September 21, Taiwan’s largest earthquake of the 20th century initiated near the small town of Chichi (23.87o N, 120.75o E, depth 7 km) and ruptured the well-mapped Chelungpu fault. The teleseismic moment tensor solution (Mo = 2.4x1027 dyne-cm) and observed surface offsets indicated a thrust mechanism on a fault shallowly dipping toward the east. The fault plane had a length of about 85 km and width of about 40 km extending from the surface to a depth of 20 km. The slip was almost pure thrust in the southern part of the fault with westward movement of the hanging wall. Farther north along the fault, the slip of the hanging wall rotates toward a northwest direction."

Co-seismic displacements, folding and shortening structures along the Chelungpu surface rupture zone occurred during the 1999 Chi-Chi (Taiwan) earthquake
A. Lin a, T. Ouchi b, A. Chen, and T. Maruyama. Tectonophysics, Vol. 330 (3-4) (2001) pp. 225-244.

Abstract
A nearly 100-km-long surface rupture zone, called Chelungpu surface rupture zone, occurred mostly along the pre-existing Chelungpu fault on the northwestern side of Taiwan, accompanying the 1999 Chi-Chi Ms 7.6 earthquake. The Chelungpu surface rupture zone can be divided into four segments based on the characteristics of co-seismic displacements, geometry of the surface ruptures and geological structures. These segments generally show a right-step en echelon form and strike NE-SW to N-S, and dip to the east with angles ranging from 50 to 85°. The co-seismic flexural-slip folding structures commonly occurred in or near the surface rupture zone from a few meters to a few hundreds of meters in width, which have an orientation in fold axes parallel or oblique to the surface rupture zone. The displacements measured in the southern three segments are approximately 1.0-3.0m horizontally and 2.0-4.0m vertically. The largest displacements were measured in the northern segment, 11.1m horizontally and 7.5m vertically, respectively. The amount of co-seismic horizontal shortening caused by flexural-slip folding and reverse faulting in the surface rupture zone is generally less than 3m. It is evident that the co-seismic displacements of the surface rupture zone are a quantitative surface indicator of the faulting process in the earthquake source fault. The relations between the geometry and geomorphology of the surface rupture zone, dips of the co-seismic faulting planes and the striations on the main fault planes generated during the co-seismic displacement, show that the Chelungpu surface rupture zone is a reverse fault zone with a large left-lateral component.