Lecture 7 Reverse faults and folds I. Environments Orthogonal convergence –Himalaya –Zagros...

Lecture 7

Reverse faults and folds I

Environments

• Orthogonal convergence– Himalaya– Zagros– Caucasus

CaucasusZagros, Elborz, etc

Himalaya

Earthquakes 1962-2003

Indian plate

Eurasian plate

African plate

Arabian plate

Elborz

Kopet Dagh

Greater Caucasus

Zagros

Lesser Caucasus

Himalaya

Earthquakes

J. Hollingsworth & M.J. Bolourchi

Tehran

J. Hollingsworth & M.J. Bolourchi

Tehran

NorthTehranFault

CaucasusZagros, Elborz, etc

Himalaya

Sub-Himalaya

Lesser-Himalaya

High-Himalaya Tibet

Gangetic plain

Topographic profile and simplified geological cross section across the

Himalaya of central Nepal.(Lave and Avouac, 2000)

A deep structure constrained from structural geology, seismic

profiles, gravity and MT sounding.

all thrust faults seem to sole at depth into the MHT

(Avouac, 2003)

Abandoned Fluvial Terraces along Trisuli River

Determining active fold growth from abandoned

river terraces

(Lave and Avouac, 2000)

Holocene slip rate on MFT : 21 +/- 1.5 mm/yr

(Lave and Avouac, 2000)

Over the long-term, shortening across the Central Nepal Himalaya is absorbed by 21 +/- 1.5 mm/yr of thrusting along a single

fault the MFT-MHT

(Cattin and Avouac, 2000)

21 +/-1.5 mm/yr

The pattern of uplift derived from incision rates, is consistent with thrusting over a mid-crustal ramp at front of the higher Himalaya. This zone of localized uplift prevents rapid headward reatreat of sream profile so that the front of the Higher Himalayan can remain linear in map view.

(Lave and Avouac, 2001)

Seismicity of Nepal Himalaya (1995-2000) (DMG)

Environments

• Orthogonal convergence• Behind-the-arc contraction zones

– Tien Shan– Andes– Papua New Guinea and Irian Jaya– Eastern Indonesia– North-Panama deformed belt– Northeastern Japan

Tien Shan

Environments

• Orthogonal convergence• Behind-the-arc contraction zones• Auxiliary faults in strike-slip systems– Coast and Transverse ranges, California

– New Zealand– Qilianshan, China

Transpressional

Transtensional

From the Southern California Integrated GPS Network, courtesy of Ken Hudnut

GPS display a component of strain not parallel to the San Andreas fault. This is accommodated mostly by thrust faults in the LA region.

Most topography in the region is the result of activity on these thrust faults

From JPL’s SRTM mission

For example, the 1987 and 1994 earthquakes alerted us to the presence of active blind thrusts within the metro region

1994

1987

Reverse faults also exist on the north side of the SA fault

Environments

• Orthogonal convergence• Behind-the-arc contraction zones• Auxiliary faults in strike-slip systems

• Shields– Australia– eastern Canada– India

Latur, India, 1993