Equivalency of geologic and geodetic rates in contractional orogens: New insights from the Pamir Frontal Thrust

Abstract

[1] Across contractional orogens, the equivalency between decadal convergence rates from geodetic GPS data and geologic shortening rates at time scales of thousands or millions of years has rarely been documented. Here, we present an example from the northern margin of Chinese Pamir, where the Main Pamir Thrust is tectonically quiescent, and recent deformation is concentrated on the Pamir Frontal Thrust (PFT). Based on dated and faulted fluvial terraces, magnetostratigraphy, and mapping, the horizontal shortening rate of the PFT is $6-7 mm/a at time scales of both $18.4 ka and $0.35 Ma, comparable to the geodetic rate of $6-9 mm/a across the same zone, implying that modern geodetic rates are a reasonable proxy for geologic rates since $0.35 Ma. Comparing this example with studies in other contractional orogens, we conjecture that a match or mismatch of geologicgeodetic rates typically depends on the time scale of observation, fault geometry, and fault mechanics. Citation: Li, T.,

Quantification of three‐dimensional folding using fluvial terraces: A case study from the Mushi anticline, northern margin of the Chinese Pamir

“…All samples were analyzed following the sensitivity‐corrected multiple aliquot regenerative‐dose protocol on the 4–11 µm grain‐size quartz fraction (Figure c) [ Lu et al ., ; Li et al ., ]. Because water absorbs some part of alpha, beta, and gamma rays that contribute to the dose rate, the impact of water content was included in the dose rate calculations [ Li et al ., ]. The samples had dried out before sampling but were saturated by water when deposited.…”

“…4–11 µm fine‐grained quartz separation and measurements follow standard methods [ Li et al ., ; Lu et al ., ]. Measurements were made in the State Key Laboratory of Earthquake Dynamics, Institute of Geology, China Earthquake Administration.…”

Coarse versus fine-grain quartz optical dating of the sediments related to the 1985 Ms7.1 Wuqia earthquake, northeastern margin of the Pamir salient, China

“…The OSL samples we collected are deposited on top of the same terrace surface, should be younger than 8.0 ka. Li et al (2012). The OSL samples were collected in stainless steel tubes (length 15-20 cm, diameter 6 cm).…”

The 2008 Nura Mw6.7 earthquake: A shallow rupture on the Main Pamir Thrust revealed by GPS and InSAR

“…However, the decadal geodetic rate for the Pamir d ecollement is much higher than the Holocene rate of >6 mm/a for the MPT, suggesting that interseismic deformation is partitioned in northern Pamir by slips on numerous imbricated faults rather than concentrated on a single thrust [5,9,13]. If this slip behavior prevails in the region, the maximum recurrent time for a 2008-type earthquake should exceed 500 years given its peak slip of about 3 m, potentially reducing the slip-deficit accumulated for subsequent greater earthquakes as occurred in the Wenchuan earthquake in 2008 [21].…”

“…The pink star with a beach ball for the focal solution shows the epicenter relocated by the first motions of P-waves recorded by the local network [12]. Black lines denote active faults from Li [13] and purple dots show regional seismicity in 2008e2012 from Sippl [14]. The locations of ALOS and EnviSAT images for the 2008 earthquake are outlined by gray rectangles.…”