Peter Molnar

University of Colorado Boulder | CUB · Department of Geological Sciences

Plain Language Summary Markedly asymmetric interseismic deformation is observed across the Altyn Tagh fault, revealing differing lithospheric rheology across the fault between northern Tibet and the Tarim Basin. We invoke a 2‐dimensional viscoelastic deformation model to interpret the GPS velocity field across the central Altyn Tagh fault and find...

Geodetically derived velocities from Central Asia show that Northern Afghanistan, the Tajik Pamir, and northwestern Pakistan all move northward with comparable large velocities toward Eurasia. Steep velocity gradients, hence high strain rates, occur only across the Main Pamir Fault zone and with lesser magnitude between the northernmost Hindu Kush...

O’Dea et al. challenged the inference that the Isthmus of Panama has been in place for the last 10 million years or more and from “an exhaustive review and reanalysis of geological, paleontological, and molecular records,” they argued for a “formation of the Isthmus of Panama sensu stricto around 2.8 Ma.” I review environmental changes since ~5 Ma...

Using a multi-proxy reduced dimension methodology we reconstruct fields of Arabian Sea summer wind-stress curl and Indian monsoon rainfall anomalies since early Holocene using SST proxies (Mg/Ca and alkenones) from 27 locations scattered across the equatorial Pacific. Reconstructions of summer wind-stress curl reveal positive anomalies of ∼ 30% gre...

Surface ruptures found east of the high peak of Bukadaban that formed during the 2001 Kunlun earthquake reveal a minor northeast–southwest‐trending graben, across which oblique approximately east–west extension occurred. Scarps along the southeast flank of the graben indicate vertical components of slip of 3–4 m, and left steps in the trace suggest...

We develop a multiproxy, reduced-dimension methodology to blend magnesium-calcium (Mg/Ca) and alkenone (U 37k) paleo sea surface temperature (SST) records from the eastern and western equatorial Pacific, to recreate snapshots of full field SSTs and zonal winds from 10 to 2 ka B.P. in 2000 year increments. Single-proxy reconstructions (Mg/Ca only ve...

The modern Asian summer monsoon is known to be affected by the modern continental geometry, orography, atmospheric composition, interglacial climate state, and orbital configuration. All of these factors, however, have undergone substantial changes since the Indian and Asian continents collided 50 million years ago. Within the framework of one gene...

A P wave speed tomogram produced from teleseismic travel time measurements made on and offshore the South Island of New Zealand shows a nearly vertical zone with wave speeds that are 4.5% higher than the background average reaching to depths of approximately 450km under the northwestern region of the island. This structure is consistent with obliqu...

An application of a simple hydrological model to likely climatic conditions of Lake Sambhar provides tighter bounds on the range of increased precipitation seen during the early- to mid-Holocene than those inferred from paleoclimatic proxies. To examine past lake levels, we developed a simple lake model, based on hydrological principles of a waters...

Correlations of 1∘ by 1∘ seasonal rainfall with Pacific sea-surface temperatures (SSTs) reveal spatially distinct teleconnections between El Niño-Southern Oscillation (ENSO) and Indian summer monsoon rainfall over the full monsoon season, as well as three sub-seasons. Over the full season (June-September), Pacific SSTs correlate with rainfall in we...

GPS measurements from sites within the Tibetan Plateau show not only east-southeast-west-northwest extension but also, more importantly, horizontal dilation throughout the interior of the plateau. Assuming conservation of volume, vertical (thinning) strain rates equal horizontal dilation rates, and they, 8.9 ± 0.8 nanostrain a−1 and 7.4 ± 1.2 nanos...

The distribution of crustal velocity over a 800-by-400 km region of the Tien Shan shows strain rates with principal contractional axes aligned perpendicular to the mountain chain, and with negligible velocity gradients in the along-strike direction. This configuration allows us to describe the dynamics by a force balance along profiles perpendicula...

The areal extent of the Maritime Continent (the islands of Indonesia and surrounding region) has grown larger by ~60% since 5 Ma. We argue that this growth might have altered global climate in two ways that would have contributed to making recurring ice ages possible. First, because rainfall over the islands of the Maritime Continent not only is he...

Dynamic topography is commonly understood to be deflection of the Earth's surface that results from convection of the mantle. Because different authors use the words “dynamic topography” differently, topography designated as dynamic may amount to only a few hundred meters or may exceed 2000 m. For most regions, however, surface heights computed on...

For a wide range of viscosity structures, convergent and downward flow of the mantle lithosphere during growth of gravitational instability induces not only thickening of overlying crust, but also concurrent horizontal extension in the upper crust. Such extension, if it occurred in the Earth, would include normal faulting of the upper crust above a...

We examine the gravitational stability of a stratified structure consisting of a low-density crust through which viscosity decreases exponentially, over a denser mantle lithosphere of constant viscosity, which in turn overlies an inviscid, slightly less dense layer like the asthenosphere. The most important aspect of the viscosity structure is the...

To understand why tropical islands are rainier than nearby ocean areas, we explore how a highly idealized island, which differs from the surrounding ocean only in heat capacity, might respond to the diurnal cycle and influence the tropical climate, especially the spatial distribution of rainfall and the thermal structure of the troposphere. We perf...

Pn travel-times from regional earthquakes recorded both by stations on New Zealand and by ocean bottom seismographs deployed offshore indicate anisotropy in the uppermost mantle beneath the region. The largest anisotropy, of ~8% (±2%, 1-σ), lies beneath the deforming part of the South Island to just off its West Coast, a zone roughly 100-200 km wid...

We exploit El Nino Southern Oscillation (ENSO) indices and moist static energy of surface air over the Indian subcontinent and surroundings as predictors of monsoon rainfall over India during early and late seasons, defined here as May 20 – Jun 15 and Sep 20 – Oct 15, respectively. Although these seasons contribute only ~22% of the entire seasonal...

Many believe that the Central American Seaway closed near 4 Ma, and that that closure led to increased salinity in the Caribbean Sea and stronger Meridional Overturning Circulation in the Atlantic, which facilitated the waxing and waning of ice sheets in the northern hemisphere. We offer an alternative explanation for Caribbean salinification. The...

Pleistocene drainage basin integration led to progressive excavation of Tertiary–Quaternary sedimentary basins along the Yellow River in the northeastern Tibetan Plateau. Cosmogenic burial dating of ancestral river deposits and basin fi ll from two key watershed divides confirms a fluvial connection between basins at 0.5–1.2 Ma, prior to excavation...

[1] New shear wave splitting measurements made from stations on and offshore the South Island of New Zealand show a zone of anisotropy 100 – 200 km wide. Measurements in central South Island and up to approximately 100 km offshore from the west coast yield orientations of the fast quasi-shear wave nearly parallel to relative plate motion, with incr...

[1] Recent studies of the northeastern part of the Tibetan Plateau have called attention to two emerging views of how the Tibetan Plateau has grown. First, deformation in northern Tibet began essentially at the time of collision with India, not 10–20 Myr later as might be expected if the locus of activity migrated northward as India penetrated the...

GPS velocities measured in the Pamir and surrounding regions show a total of ~30 mm/yr of northward relative motion between stable Pakistan and Eurasia. The convergence budget is partitioned into 10–15 mm/yr of localized shortening across the Trans-Alai Thrust, which bounds the Pamir on the north, consistent with southward subduction of intact lith...

[1] Surface topography and associated gravity anomalies above a layer resembling continental lithosphere, whose mantle part is gravitationally unstable, depend strongly on the ratio of viscosities of the lower-density crustal part to that of the mantle part. For linear stability analysis, growth rates of Rayleigh-Taylor instabilities depend largely...

We determined vertical components of slip rates of 0.22 ± 0.03 mm a–1 for the Jiayuguan fault and 0.11 ± 0.03 mm a–1 for the Jintanan Shan fault, which lie along the northeastern edge of the Tibetan Plateau and in the western Hexi Corridor (Northern Qilian Shan, China). We used structural investigations, air-photo imagery analysis, topographic prof...

We have examined the spatial and temporal distributions of some 570 reports of changes in ground water and 670 reports of anomalous animal behavior in the three months before the Haicheng earthquake (4 February 1975, M=7.3). These changes and anomalies were reported from a very large area, extending more than 150 kilometers in nearly all directions...

Based on field investigations, aerial-photos morphological analysis, topographic profiling, and optically stimulated luminescence (OSL) dating of alluvial surfaces, we estimate vertical components of the slip rate along the South Heli Shan thrust Fault, which lies on the northern margin of the Hexi corridor and the northeastern edge of the Tibetan...

[1] Despite recent challenges, conventional wisdom has held that heating over the Tibetan Plateau leads to increased Indian summer monsoon rainfall via enhancement of cross-equatorial circulation aloft, and a concurrent strengthening of both the Somali Jet and westerly winds that bring moisture to southern India. We show that such heating, quantifi...

Many geologic observations suggest that the eastern portion of the Tibetan Plateau has expanded eastward and grown in height over the past 15-10 Ma, and other observations suggest that climate over the northwestern Indian subcontinent (“NW India”) became more arid between ˜11 and 7 Ma. We suggest that they are linked: higher terrain increased orogr...

By regressing simple, independent variables that describe climate and tectonic processes against measures of topography and relief of 69 mountain ranges worldwide, we quantify the relative importance of these processes in shaping observed landscapes. Climate variables include latitude (as a surrogate for mean annual temperature and insolation, but...

For central India and its west coast, rainfall in the early (15 May–20 June) and late (15 September–20 October) monsoon season correlates with Pacific Ocean sea-surface temperature (SST) anomalies in the preceding month (April and August, respectively) sufficiently well, that those SST anomalies can be used to predict such rainfall. The patterns of...

Multibeam bathymetric surveys east of the South Island of New Zealand yield images of submarine volcanoes and pockmarks west of Urry Knolls on the Chatham Rise, and evidence of submarine erosion on the southern margin of the Chatham Rise. Among numerous volcanic cones, diameters of the largest reach c. 2000 m, and some stand as high as 400 m above...

Magnetostratigraphy of sedimentary rock deposited in the Chaka basin (north-eastern Tibetan Plateau) indicates a late Miocene onset of basin formation and subsequent development of the adjacent Qinghai Nan Shan. Sedimentation in the basin initiated at ∼11 Ma. In the lower part of the basin fill, a coarsening-upward sequence starting at ∼9 Ma, as we...

Seismologist who helped demonstrate that Earth's continents move constantly.

By regressing simple, independent, variables that describe climate and tectonic processes against measures of topography and relief of 69 mountain ranges worldwide, we quantify the relative importance of these processes in shaping observed landscapes. Climate variables include latitude (as a surrogate for mean annual temperature and insolation, but...

Measurements at ∼400 campaign-style GPS points and another 14 continuously recording stations in central Asia define variations in their velocities both along and across the Kyrgyz and neighboring parts of Tien Shan. They show that at the longitude of Kyrgyzstan the Tarim Basin converges with Eurasia at 20 ± 2 mm/yr, nearly two thirds of the total...

A large fraction of major intracontinental strike-slip faults, defined here as those slipping at rates of ~10 mm/yr or more, lie adjacent to relatively strong regions, such as oceanic lithosphere or Precambrian shields. We suggest that such faults form adjacent to discontinuities in strength, because strain in a continuous medium must concentrate n...

Recordings in western Tibet of Rayleigh and Love waves at periods less than 70 s from aftershocks of the 2008 Sichuan earthquake cannot be matched by an isotropic velocity model beneath Tibet. These intermediate-period Rayleigh and Love waves require marked radial anisotropy in the middle crust of Tibet, with the vertically polarized S-waves propag...

We use ten years of GPS data from nine continuous and six semi-continuous GPS stations in a transect across the Southern Alps to measure rates of relative vertical movement with typical 1σ uncertainties of 0.3–0.5 mm/yr. The estimated vertical rates define a fairly smooth profile across the range, with the highest rates of ∼5 mm/yr found near the c...

Terra Nova, 22, 180–187, 2010 We constrain the slip rate for the frontal thrust of the Qilian Shan (north-eastern Tibet) by combining structural investigations, satellite imagery, topographic profiling, and 10Be exposure dating. We surveyed two terrace levels, and from each, we took 6–7 samples in profiles dug to depths of 2 m. These constrain inhe...

We compare the geologic histories, the deep structures, and the present-day kinematics of deformation of the Himalaya and the adjacent Tibetan Plateau with those of the Zagros and Iranian Plateau to test geodynamic processes of continental collision. Shortly after India and Arabia collided with Eurasia, horizontal shortening manifested itself by fo...

Although geomorphic observations suggest that the Sierra Nevada has tilted so that the crest has risen 1-2 km since late Miocene time, deuterium and oxygen-18 isotope concentrations in Cenozoic geologic materials decrease eastward across California and Nevada similarly to those in modern, orographically induced precipitation, as if little change in...

With a compilation of topographic, geomorphic, tectonic, and climatic characteristics of more than 50 mountain belt worldwide, we explore the correlations among various characteristics. Topographic data, from the GTOPO30 DEM, include several parameters: maximum elevation, mean elevation, and maximum averaged elevation, calculated above sea level an...

Prevailing opinion assigns the Tibetan Plateau a crucial role in shaping Asian climate, primarily by heating of the atmosphere over Tibet during spring and summer. Accordingly, the growth of the plateau in geologic time should have written a signature on Asian paleoclimate. Recent work on Asian climate, however, challenges some of these views. The...

Variability in oxygen isotope ratios collected from speleothems in Chinese caves is often interpreted as a proxy for variability of precipitation, summer precipitation, seasonality of precipitation, and/or the proportion of 18 O to 16 O of annual total rainfall that is related to a strengthening or weakening of the East Asian monsoon and, in some c...

Thinning of mantle lithosphere due to Rayleigh-Taylor instability can be a mechanism for triggering continental magmatism near active or recently active plate boundaries. We consider whether it is also plausible as a mechanism for intracontinental magmatism, several hundred kilometers from active subduction or rifting. We perform two-dimensional Ra...

[1] Convergence of 29 ± 1 mm/yr between the NW corner of the Indian plate and Asia is accommodated by a combination of thrust and strike-slip faulting on prominent faults and apparent distributed deformation within the Hindu Kush, Pamir, South Tien Shan and Kohistan Ranges. An upper bound to the slip rate of known faults is obtained by ignoring dis...

Crustal deformation along the present-day northern margin of the Tibetan Plateau has occurred since mid to late Eocene time, soon after India collided with Eurasia. Assuming that on these distance and time scales the lithosphere can be approximated using a thin viscous sheet, we show that far-field lithospheric deformation caused by an indenting bo...

In October 2008 two Mw 6.4 earthquakes preceded a two-month-long aftershock sequence in the Chiltan region of N. Baluchistan 50 km northeast of Quetta. InSAR data combined with teleseimic body wave modeling and campaign GPS data indicate that the two mainshocks occurred at 10-13 km depth in a fold-and-thrust belt on segments of a northwest trending...

We examine differences between the Zagros and Himalaya, where the collisions of Arabia and India with Eurasia have built mountain belts, and between their adjacent Iranian and Tibetan Plateaus to test geodynamic processes. Whereas the thrusting of fragments of India's northern continental margin atop one another and onto India's strong lithosphere...

A marked contrast in strength (or viscosity) within a continuously deforming zone can lead to concentration of shear strain in the weaker material adjacent to the boundary between them, but localization comparable to the width of the Altyn Tagh shear zone requires an additional weakening process. During numerical experiments on a thin viscous sheet...

Reconstructions of the relative positions of the India and Eurasia plates, using recently revised histories of movement between India and Somalia and between North America and Eurasia and of the opening of the East African Rift, show that India's convergence rate with Eurasia slowed by more than 40% between 20 and 10 Ma. Much evidence suggests that...

Combining the terrace riser offsets with terrace ages dated by 14C, OSL and 10Be techniques, we determine average strike slip rates of Elashan and Riyueshan faults, two north-northwest-trending strike-slip faults along the western and eastern sides of the lake Qinghai, northeastern margin of the Tibetan plateau, to be about 1.0 ± 0.2 mm/yr and 1.2...

A compilation of topographic, geomorphic, tectonic, and climatic characteristics of more than 50 mountain belt worldwide shows a variety of weak and strong correlations between various characteristics. Topographic data, from the GTOPO30 DEM, include several parameters: maximum elevation, mean elevation, and maximum averaged elevation, calculated ab...

The Qilian Shan, with peak elevations >5500 m, seems to have been built largely during late Miocene time (e.g. Tapponnier et al., 2001) and continues to be seismically active (Hetzel et al., 2004), having produced the very large the Gulang earthquake in 1927 (M=8.0) (e.g., Zheng et al., 2005). Associated deformation is partitioned into thrust fault...

Thinning of the lower lithosphere due to Rayleigh--Taylor instability can be a source for continental magmatism near active or recently active plate boundaries. We consider whether it is also plausible as a mechanism for intra-continental magmatism, several hundred kilometers from active subduction or rift zones. For depth varying viscosity, Raylei...

The separation of zones of apparent downwelling flow at the ends of the Sierra Nevada suggests a relatively large wavelength (˜500 km) of unstable growth, but Rayleigh-Taylor instabilities for plausible rheological structures with a fixed top boundary condition require much shorter wavelengths (<100 km) for maximum growth rates. To understand this...

The Research Station of the Russian Academy of Sciences in Bishkek, Kyrgyzstan, hosted its fourth international symposium in June to celebrate both the thirtieth anniversary of the station and the tenth anniversary of the International Research Center-Geodynamic Proving Ground (IGRC). The IGRC, whose base institution is the research station, was es...

1] What role did the closing of the Central American Seaway play in enabling continental ice sheets to wax and wane over North America and Fennoscandia? A summary of relevant evidence presented here permits a causal relationship between them but can be interpreted to show none. The common denominator of such evidence is the approximate simultaneity...

The separation of zones of apparent downwelling flow at the ends of the Sierra Nevada suggest a relatively large wavelength (~500km), but Rayleigh-Taylor instability for plausible rheological structures with a fixed top boundary condition require much shorter wavelength (<100km). To understand this difference we perform analytical and numerical pla...

Abstract Reconstructions of the relative positions of the Indian, African, and Antarctic plates and their uncertainties are given for the times of selected magnetic anomalies that could be identified on adjacent pairs of these plates. Among the most certain reconstructions are those for the Antarctic and African plates, which can be determined dire...

The geological features now exposed at Mormon Point, Death Valley, reveal processes of extension that continue to be active, but are concealed beneath the east side of Death Valley. Late Cenozoic sedimentary rocks at Mormon Point crop out in the hangingwall of the Mormon Point low-angle normal fault zone, a fault zone that formed within a releasing...

Vitaly Khalturin, a pioneering seismologist with encyclopedic knowledge of regional seismic signals and a mentor and friend of seismologists around the world, died on 17 April 2007 in Stanford, California, four days after suffering a major stroke.⇓ ![][1] Vitaly Khalturin (second from left) in 1976, working at home with graduate students in Garm...

o Both Global Positioning System (GPS) measurements and studies of Late Quaternary faulting are consistent with a slip rate of ∼10 mm/yr along the central segment of the Altyn Tagh Fault and a systematic decrease in that rate toward the eastern end of the fault. Dates of terraces above and below laterally offset terrace risers yield bounds on Quate...

Paleoceanographic data from sites near the equator in the eastern and western Pacifi c Ocean show that sea-surface temperatures, and apparently also the depth and tempera- ture distribution in the thermocline, have changed markedly over the past ~4 m.y., from those resembling an El Niño state before ice sheets formed in the Northern Hemisphere to t...

For virtually every mountain belt and high plateau, as well as for many topographically minor features, a credible, if not outstanding, geologist has asserted that that high terrain rose abruptly in Pliocene and/or Quaternary time. Such suggestions rely on a variety of observations that include paleobotanical finds of plant organs resembling those...

We argue that by fracturing rock, not by raising it relative to base level, tectonics plays its most important role in causing rapid incision of valleys and rapid erosion of hillslopes. Tectonic deformation riddles the upper crust with fractures, which not only provide avenues for water flow and thus promote weathering and further disintegration of...

The earliest credible account on the age of the Earth came from William Thomson, better known as Lord Kelvin and from his assistant John Perry. They estimated the Earth age by taking into account heat measurements. Kelvin used the Fourier transformation which had shown that diffusion equation, in which the rate of change of temperature at a point i...

Many readers know the tale of how William Thomson (later Lord Kelvin) calculated the age of the Earth from physical prin- ciples and adhered for over 50 years to an estimate that was far younger than geologists' estimates, despite the virtually unani- mous opposition of the geological community of the time. The prevalent version of this tale allege...

The growth of the gravitational instability associated with a dense layer overlying a lighter layer, Rayleigh-Taylor instability, depends strongly on the constitutive law relating stress and strain rate. We analyse Rayleigh-Taylor instability to understand how the stress dependence of viscosity might affect convective instability associated with th...

The calculation of the uncertainty in an estimated rotation requires a parametrization of the rotation group; that is, a unique mapping of the rotation group to a point in 3-D Euclidean space, R3. Numerous parametrizations of a rotation exist, including: (1) the latitude and longitude of the axis of rotation and the angle of rotation; (2) a represe...

1] The rapid rise of the central Andean plateau between $10 and 6.8 Ma implies that mantle lithosphere, including eclogitized lower crust, was removed from beneath the region in that time interval; we infer from that removal that the average viscosity coefficient of mantle lithosphere was quite low when removal occurred. Using scaling laws for the...

The Cenozoic reorganization of islands in the Maritime Continent region of the tropical western Pacific may have increased the amount of land surface area, changed the distribution of sea surface temperature (SST), and consequently provided a necessary condition for the onset of the Walker Circulation. Precipitation rates over the Maritime Continen...

The high elevation and deep incision of the Alps have traditionally been used as an argument for recent tectonic activity that has elevated the belt and increased erosion rates. Normal faulting and horizontal extension, however, dominate current tectonic activity, and isostatic compensation of thinning crust should lead not to increased but to decr...

Near the threshold of stability, an intrinsically denser fluid heated from below and underlying an isothermal fluid can undergo oscillatory instability, whereby perturbations to the interface between the fluids rise and fall periodically, or it can be mechanically stable and in thermal equilibrium with heat flux extracted by small-scale convection...

We compare the geodetic deformation field in the region of the Eastern Syntaxis of the Indian-Eurasian collision with solutions from the thin viscous sheet model of continental deformation to constrain on the vertically-averaged rheology and deformation style of the lithosphere. The deformation is defined in terms of the vorticity field calculated...

The determination of palaeo-elevation has emerged in the past 15 years as an important tool for constraining physical processes that govern the formation of mountain belts. Rowley and Currie report palaeo-elevations for the Lunpola basin within the Tibetan plateau and claim that these elevations are incompatible with 'mantle-thickening models' for...

We examined effects of surface erosion on the growth of periodic instabilities (e.g., folding, boudinage) under regional compression, because these phenomena can be treated semi-analytically, which allows a direct physical interpretation. To understand topographic evolution, it is necessary to examine this when topography starts to grow. In additio...