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We present the crustal fault model for Alaska, based on geologic observations, as a primary input for the 2023 revision of the U.S. Geological Survey National Seismic Hazard Model (NSHM). We update the 2013 Alaska Quaternary fault and fold database (Koehler, 2013) with subsequent findings to produce a simplified model of 105 fault sections and four fault zone polygons with basic geologic parameters including slip sense and rate. Significant updates from prior maps include: 1) A slip rate of ~53 mm/yr on the Queen Charlotte Fault system indicating it accommodates all of the plate boundary motion. 2) Quantified long-term slip rates on megathrust splay faults in the southern Prince William Sound region and near Kodiak Island. 3) Improved details of structures in the Chugach-St. Elias orogen. 4) Revised characterization of Castle Mountain Fault from right-lateral slip to a predominantly reverse fault. 5) Improved Interior Alaska tectonic models that clarify relationships between the Denali Fault, Totschunda Fault, and thrust faults on both sides of the Alaska Range. 6) Identified large earthquake sources in the eastern Brooks Range. 7) Omission of the Chatham Strait section of the Denali Fault. We also describe the growing body of Alaskan lacustrine paleoseismic records of strong shaking, which may offer a test of ground motion recurrence predicted by the 2023 NSHM for crustal, megathrust, and intraslab events. The fault model underscores that the collision of the Yakutat microplate is the dominant driver of active crustal faulting in most of Alaska.

Rich Briggs1, Robert C. Witter2, Jeffrey T. Freymueller3, Peter M. Powers1, Peter J. Haeussler2, Stephanie L. Ross4, Tina Dura5, Simon E. Engelhart6, Richard D. Koehler7, Hong Kie Thio81 U.S. Geological Survey, Geological Hazards Science Center, Golden, CO, USA2 U.S. Geological Survey, Alaska Science Center, Anchorage, AK, USA3 Department of Earth and Environmental Sciences, Michigan State University, East Lansing, MI, USA4 Pacific Coastal and Marine Science Center, US Geological Survey, Moffett Field, CA, USA5Department of Geosciences, Virginia Tech, Blacksburg, VA, USA6Department of Geography, Durham University, Durham, UK7Nevada Bureau of Mines and Geology, University of Nevada, Reno, Reno, NV, USA8 AECOM, Los Angeles, CA, USACorresponding author: Rich Briggs (rbriggs@usgs.gov)Key Points:We present earthquake recurrence estimates from geologic and geodetic data for the Alaska-Aleutian subduction zoneRecurrence estimates provide constraints for seismic hazard modelsThe recurrence estimates indicate that the rates of Mw≥ 8 ruptures are higher than previously inferred west of Kodiak Island

Running Head: Rock uplift west of the Fairweather fault, AlaskaR.C. Witter1, H.M. Kelsey2, R.O. Lease1, A.M. Bender1, K.M. Scharer3, and P.J. Haeussler1, and D.S. Brothers41U.S. Geological Survey Alaska Science Center, Anchorage, AK, USA2Department of Geology, Cal Poly Humboldt, Arcata, CA, USA3U.S. Geological Survey Earthquake Science Center, Pasadena, CA, USA4U.S. Geological Survey, Pacific Coastal and Marine Science Center, Santa Cruz, CA, USAAbstract [286/300 words]Contraction along the Yakutat-(Pacific)-North America plate boundary drives extreme rock uplift along Earth’s fastest slipping (≥49 mm/yr) ocean-continent transform fault, the Fairweather fault. Between Icy Point and Lituya Bay, the near-vertical Fairweather fault focuses rock uplift and rapid right-lateral slip by accommodating both vertical and fault-parallel strain during ruptures with a substantial vertical-slip component and separate, predominantly strike-slip events. We use 1.0 m resolution digital elevation models and offshore seismic reflection profiles to map active faults, uplifted marine and fluvial terraces, and document past reverse fault earthquakes with maximum 3–5 m of coseismic uplift per event. Radiocarbon and luminescence dating provide timing to estimate 4.6–9.0 mm/yr Holocene rock uplift rates, which match 5–10 km/Myr Quaternary exhumation rates estimated from thermochronometry. These unusually high uplift rates result from plate-boundary strain that is partitioned onto reverse faults that form, together with the steeply dipping Fairweather fault, a 10-km-wide, asymmetric, positive flower structure along a 20°, ~30-km-long restraining double bend in the Fairweather fault. The principal reverse fault in the flower structure is the offshore, blind Icy Point-Lituya Bay fault, which ruptures no more than every 460–1040 years evidenced by uplifted Holocene marine shorelines. Evaluated over a range of dips, the uplift on this reverse fault implies maximum 3.1–10 m dip slip per event and estimated earthquake magnitudes of Mw 7.0–7.5. Our model implies oblique slip on the Fairweather fault at seismogenic depths with and without co-rupture on the reverse fault. Oblique slip on the Fairweather fault is evident where it vertically offsets fluvial and marine terraces by >25 m, strikes >20° west of plate boundary motion, juxtaposes near-surface rocks of different strength, and where the Yakutat block collides obliquely into North America.

Intraslab earthquakes do not produce primary paleoseismic evidence at the Earth’s surface, making efforts to develop an event chronology challenging. However, the strong ground motion from intraslab events may initiate gravity-driven turbidity flows in subaqueous basins; the resulting deposits (turbidites) can provide a paleoseismic proxy if the conditions that initiate these flows are known. To better constrain the initiating conditions, we use two recent intraslab earthquakes in southcentral Alaska, the Mw 7.1 November 30, 2018, Anchorage and the Mw 7.1 January 24, 2016, Iniskin earthquakes, as calibration events. Through a multi-lake investigation spanning a range of shaking intensities and based on a combined geological and geophysical dataset, we document the occurrence, or absence, of earthquake-generated turbidity flows from these two earthquakes. The 2018 and 2016 earthquakes are recorded by centimeter-scale turbidites that can be differentiated from climatically generated deposits, as well as other seismic sources (i.e., the 1964 Alaska megathrust earthquake) based on deposit thickness, sedimentological properties, and deposit age. We show that a Modified Mercalli Intensity (MMI) of ~V-V1/2 is the minimum shaking intensity required to generate localized sediment remobilization from deltaic slopes, and a MMI of ~V1/2 is required to produce a deposit of sufficient thickness that a seismic origin can be confidently assigned. Deltaic slopes are the major source of remobilized sediment that record the 2018 and 2016 events, however sediment from non-tributary sourced basin slopes may become remobilized in steep-sloped, high sedimentation areas, and under elevated shaking intensity. The documentation of seismically generated deposits in quick succession (~2 years) with diagnostic features that can be assigned to the seismic source highlights the utility of using recent earthquakes as calibration events to investigate the subaqueous response to strong ground motion. 

Jeff Apple Benowitz1, Michael Everett Mann21 GeoSep Services, 1521 Pine Cone Road, Moscow, ID, USA2 Department of Earth, Environmental and Planetary Sciences, Brown University, Providence, RI, USACorresponding author: Jeff Apple Benowitz (jeffapplebenowitz@gmail.com)AbstractLong-lived magmatic arcs theoretically should migrate large trench perpendicular distances as convergent margin configurations and slab geometry vary over time, however many arc-magmatic belts are spatially localized over 10’s of millions of years. We document, by compiling published crystallization geochronology data for southern Alaska (6485 total bedrock and single grain detrital ages combined), that since ca. 100 Ma, arc magmatism has been localized along the Alaska Range suture zone, at times over 500-km inboard. However, since ca. 100 Ma incoming subducting slab characteristics, beneath mobile southern Alaska and convergent margin configurations, varied greatly and include both normal oceanic plate and oceanic plateau subduction, plate vector changes, oroclinal bending and reconfiguration of trench shape, terrane accretion, long distance translation and a Paleocene slab break off/slab window event. Therefore, it is inferred that inherited upper-plate lithospheric shape and heterogeneity must control in part the geometry of the subducting slab below a mobile southern Alaskan margin through hydrodynamic (viscous) mantle wedge “suction” forces. Additionally, crustal thickness heterogeneity may preferentially focus magma ascent through melt ponding along Moho offsets, and upper-plate lithospheric-scale strike-slip faults may be acting as passive and active conduits for arc magmatism. Inherited upper-plate controls on slab geometry could be a factor localizing arc magmatism along other long-lived convergent margin settings.

Plate Motion Change at ca. 6 MaJacob L. Rosenthal1, Paul G. Fitzgerald1, Jeffrey A. Benowitz2, James R. Metcalf2, Paul M. Betka31Department of Earth and Environmental Sciences, Syracuse University , Syracuse NY 13244, USA2Department of Geological Sciences, University of Colorado Boulder , Boulder Co 80309, USA3Atmospheric, Oceanic, and Earth Sciences Department , George Mason University, Fairfax VA 22030, USACorresponding author: Jacob Rosenthal (jlrosent@syr.edu)

The prediction of how ice crystals form represents one of the great conundrums in the atmospheric sciences with important implications for the hydrological cycle and climate. Ice-nucleating particles (INPs), typically consisting of sub-and supermicrometer-sized aerosol particles which can be inorganic, organic, biogenic, or biological, initiate heterogeneous ice nucleation processes leading to ice crystal formation. Heterogeneous ice nucleation commences on the nanoscale at the substrate surface and depends on ambient temperature and humidity. Microanalysis techniques are uniquely suited to examine the physicochemical features of the INPs under relevant atmospheric conditions thereby advancing our understanding of the principal processes that promote ice nucleation. In the atmosphere ice crystals experience growth and sublimation resulting in complex microscopic morphologies which, in turn, impact the ice crystal's properties. This chapter provides an overview of microanalysis techniques employed in either a multimodal or in situ manner, which shed light on the atmospheric heterogeneous ice nucleation process and how these techniques are applied to explore the complex morphologies of ice crystals. The first section introduces the various atmospheric ice nucleation pathways, provides a brief outline of the underlying nucleation theory demonstrating that nucleation proceeds on the nanoscale, and describes the different ice crystal habits of growth. Section two provides an overview of the microanalysis techniques and experiments to study INPs or ice-nucleating substrates including multimodal instrument approaches followed by in situ ice nucleation studies. Examples of techniques include Raman, atomic force, electron, and X-ray microscopy with discussion of the techniques’ unique capabilities to examine the physical and chemical properties of the ice-nucleating substrate. The third section presents electron microscopy studies of ice crystals during growth and sublimation displaying the morphological complexities of ice crystals. Lastly, section four discusses typical experimental requirements including sample sizes, radiation effects, and the role of standard INPs.

Madhav Patel and Athanasios K. Karamalidis*Energy and Minerals Engineering, Pennsylvania State University, State College, PA 16802 USA (*correspondence: akk5742@psu.edu)

Efthymios Balomenos1, Panagiotis Davris1, Dimitrios Panias1, Ioannis Paspaliaris1Laboratory of Metallurgy, National Technical University of Athens, Zografos Campus, GreeceEmail: thymis@metal.ntua.grBauxite Residue‘Bauxite Residue’ (BR) refers to the insoluble solid material, generated during the extraction of alumina (Al2O3) from Bauxite ore using the Bayer process. When bauxite ore is treated with caustic soda, the aluminium hydroxides/oxides contained within, are solubilized, with approximately 50% of the bauxite mass being transferred to the liquid phase, while the remaining solid fraction constitutes the -bauxite- residue.Active lime is usually added during digestion to control and reduce caustic soda and alumina losses from the formation of desilication products.. The solid-liquid separation after ore digestion takes place in thickeners and washers, resulting in the formation of a red-colored bauxite residue slurry (approx. 50% solids) which was previously termed ‘red mud’. Nowadays many plants use, as a final step of slurry treatment, high pressure filtration (the most efficient method of alkali recovery), in which the bauxite residue slurry is pressed to remove the maximum of remaining liquor and produce a compact filtercake with a relative humidity of 25-30%.It is estimated that for each ton of alumina produced 1.0- 1.5 tons of solid residue (on a dry basis) is generated depending on the initial bauxite ore grade and alumina extraction efficiency (Evans 2016). Bauxite residue consists of of various metal oxides of Fe, Al, Ti, Si, Ca, Na, V, Ga (depending on the initial chemical composition of the bauxite ore) along with inclusions of unwashed sodium aluminate solution.As the global demand for primary aluminium metal increases so will the BR production, currently in excess of 150 million tons per year worldwide (Power et al. 2011). This is generated at more than 100 active alumina refining plants worldwide. In addition, there are at least another 50 closed legacy sites, so the combined stockpile of bauxite residue at active and legacy sites is estimated at three thousand million tons. ( World Aluminium and the European Aluminium Association, 2015)The primary aluminium industry has always focused on discovering potential applications for BR utilization. The vast amount of research and studies on BR utilisation is justified by more than 734 patents since 1964. Possible applications can broadly be broken down into various categories, such as cement and building materials production, iron production, trace element (Ga, REE, V,etc.) recovery, use as soil amelioration, landfill capping, acid mine drainage treatment and others (Evans 2016). The recent REE crisis fueled significant research effort in recovering the REE that are found in some BRs in concentrations between 1 - 2 kg of total REE / t of BR. Given the large quantity of the annual BR production, the total amount of contained REE becomes significant and could cover part of the global REE demand (Balomenos et al., 2017a). Furthermore, while the treatment of BR for the recovery of REEs does not solve the BR deposition problem, as the volume of the waste remains practically unaffected, it does help in the economic viability of holistic processing flowsheet seeking to achieve near zero-waste through multiple processing steps (Balomenos et al., 2017b).Rare Earths in Bauxite ResidueThe bauxite ore is one of the factors that affect the concentration of REE in bauxite Residue. Bauxites are classified in three categories, lateritic bauxites (88%), karstic bauxites (11,5%) and Tikhvin type bauxites (0,5%) (Bardossy, 1982; Bárdossy and Aleva, 1990). Karstic bauxites are mainly found in Europe, Jamaica, Russia and China. The karstic bauxites contain higher concentrations of REE than the lateritic bauxites. REE are detected in bauxite ore as fluorcarbonate or phosphate minerals which are very similar to the main industrial minerals of REE (bastnaesite - monazite) (Li et al., 2013; Mouchos et al., 2017; Ochsenkühn-Petropulu 1995; Vind et al., 2018a). It has also been reported that in the Bayer process REE end up in the BR in 2:1 ratio, compared to the initial bauxite ore. (Derevyankin et al., 1981; Ochsenkühn-Petropulu et al., 1994; Wagh and Pinnock, 1987).The worldwide typical concentration of REE in BR is 800-2500 mg/kg and is related to the initial bauxite ore and the operating conditions of the Bayer process (Deady et al., 2018). Recent research shows that REE in BR can be found in secondary mineral phases produced by the Bayer process, known as the desilication product (DSP). DSP is the result of the silicon removal from the aluminate solution during the leaching of the bauxite ore, as silicon is major pollutant for the final alumina product. Presence of REE in the DSP can be attributed to REE from the bauxite ore being dissolved in the Bayer process; these REE are incorporated into the newly formed DSP mineral matrix that contains a mixture of Fe, Ti, Si, Al Ca and Na ions (Vind et al., 2018a).Scandium (Sc) often differs from the other REE behavior. Especially in lateritic bauxites and their corresponding BR, it is often correlated with iron and titanium and zircon minerals (Vind et al., 2018a) (Liu et al., 2018; Zhang et al., 2017), which for the most part are unaffected by the Bayer process. This is also confirmed by the laterite deposits in Australia and the Greek BR (Chassé et al., 2016) where the main mineral, with high concentration of Sc is goethite (Vind et al., 2018b). However, there are cases of BR ,where Sc is found to be related to larger extent to the soluble Al-bearing minerals, as is reported by Russian researchers (Suss et al., 2018).Published chemical analysis and leaching studies of bauxite residue focus on the concentration of Sc, because Sc represents 95% of REE’s financial values found in BR (case of Greek Bauxite, reported by Ochsenkühn-Petropoulou et al., 2002). Table 1 presents the Sc concentration in different Bauxite Residues worldwide as reported in literature.Table 1 Concentration of Scandium in Different Bauxite Residues

Significant advances have been made over the last two decades in constraining the structure of the continental lithosphere in Alaska, particularly with the EarthScope USArray seismic data collection efforts. This paper distills recent seismic models in Alaska and western Yukon (Canada) and relates them to major faults and tectonic terranes. We synthesize results from eight shear-wave velocity models and seven crustal thickness models. Through objective clustering of seismic velocity profiles, we identify six different velocity domains, separately for the crust (at the depth range of 10-50 km) and the mantle (at the depth range of 40-120 km). The crustal seismic domains show strong correlations with average crustal thickness patterns and the distribution of major faults and tectonic terranes. The mantle seismic velocity domains demonstrate signatures of major faults and tectonic terranes in northern Alaska while in southern Alaska the domains are primarily controlled by the geometry of the subducting lithosphere. The results of this study have significant implications for the tectonics and geodynamics of the overriding continental lithosphere from the margin to the interior. This synthesis will be of interest to future studies of Alaska as well as other modern and ancient systems involving convergent margins and terrane accretions.

This introductory chapter discusses the atmospheric subgrid processes ─ collectively called "fast 11 physics" or "fast processes", and their parameterizations in large scale atmospheric models. It 12 presents a brief historical progression of the parameterization of fast processes in numerical 13 models. Despite great efforts and notable advances in understanding, progress in improving fast 14 physics parameterizations has been frustratingly slow, the underlying reasons for which are 15 explored. To guide readers, this chapter describes the main objectives and scope of this book and 16 summarizes each chapter. 

Water quality in rivers is influenced by natural factors and human activities that interact in complex and nonlinear ways, which make water quality modelling a challenging task. The concepts of complex networks (CN), a recent development in network theory, seem to provide new avenues to unravel the connections and dynamics of water quality phenomenon, including clandestine teleconnections. This study aims to explore the spatial patterns of water quality using the CN concepts, at both catchment scale and larger national scale. Three major water quality parameters, i.e. dissolved oxygen (DO), permanganate index (COD Mn), and ammonia nitrogen (NH 3-N) are considered for analysis. Weekly data over a period of 12 years (since 2006) from 91 monitoring stations across China are analysed. Degree centrality and clustering coefficient methods are employed. The results show that the degree centrality and clustering coefficients values for water quality indicators is DO > NH 3-N > COD Mn at both basin scale and national scale. Since COD Mn is more sensitive to the upstream point source pollution, as it depends upon the locality and human activities, it leads to a higher heterogeneity of CN indexes even among spatially closer stations. NH 3-N comes next due to the identical pollution level and degradation process in a certain spatial extension. Meanwhile, DO shows good regional connectivity in line with the strong diffusivity. However, the CN characteristic is relatively inconspicuous in large basins and nationwide scale, which indicates the regional impact on water quality fluctuation and CN analysis. These original findings boost a comprehensive understanding of water quality dynamics and enlighten novel methods for environment system analysis and watershed management.

Tethyan evolution is characterized by cyclical continent-transfer from Gondwana to the continents in the Northern Hemisphere, similar to a “one-way” train. Subduction has been viewed as the primary driver of transference. Therefore, it is crucial to understand the tectonic evolution of all past subduction zones that occurred along Eurasia’s southern margin. We studied the earliest known eclogite located at the Neo-Tethyan suture in the Iranian segment. A prograde-E-MORB-like eclogite reached a peak metamorphic condition of 2.2 GPa and 560°C, at 190 ± 11 Ma (1 rutile U-Pb ages), which constrains the youngest age for subduction initiation of the Neo-Tethyan slab. Combined with regional magmatic and structural data, the oldest age for Neo-Tethys subduction initiation is 210–192 Ma, which is younger than the Paleo-Tethyan closure time of 228–209 Ma. These data, used with previous numerical modeling, supports collision-induced subduction initiation. The collision-induced force, together with the Paleo-Tethyan subduction driven-mantle flow, is likely to have exploited weak inherited structures from earlier Neo-Tethyan rifting, resulting in a northward directed subduction zone along the southern margin of Central Iran Block.

Compressional and contractional tectonics are of interest to various researchers, from rock mechanics and engineering to those studying the hazards, dynamics, and evolution of plate boundaries. We summarize here the terminology regarding deformation associated with compressional and contractional tectonics. We describe the now largely discarded geosyncline theory, which has its roots in contraction. Today, plate tectonics is the primary theory for explaining the processes shaping the Earth, including earthquakes, volcanoes, and mountain ranges. We emphasize the importance of subduction zones, the most extensive recycling system on the planet, and suture zones, complex boundaries marking the collision zone between two plates. The effects and hazards associated with convergent and collisional plate boundaries are felt far afield and for long distances.

Preface Many physical processes that influence Earth's climate and weather occur on spatial (temporal) scales smaller (shorter) than typical grid sizes (time steps) of general circulation models, and thus must be parameterized. Computer models are essential tools for understanding atmospheric phenomena and for making accurate predictions of any changes in the Earth's climate, weather, and resources of renewable energy resulting from anthropogenic activities that generate greenhouse gases and particulates into the atmosphere. This book focuses on the atmospheric subgrid processes ─ collectively called fast physics ─by reviewing and synthesizing relevant physical understanding, parameterization developments, various measurement technologies, and model evaluation framework. The publication is divided into three parts, containing seventeen chapters (Chapters 2-17) to reflect and synthesize the multiple aspects involved. The first chapter briefly introduces the historical development of fast physics parameterizations and the involved complexities; the last chapter summarizes emerging challenges, new opportunities and future research directions. Part I deals with major subgrid processes, with eight chapters (Chapters 2-9) each covering different processes more or less in the conventional compartmentalized format with an emphasis on individual processes, including but, not limited to radiative transfer, aerosols, and aerosol direct & indirect effects, entrainment-mixing processes, their microphysical influences, convection & convective clouds, stratiform clouds such as stratus and stratocumulus clouds, planetary boundary layer processes, land surface and interactions with atmosphere, and gravity waves. On top of the conventional treatments, some promising ideas/approaches have recently emerged to unify the treatment of individual processes and thus allows for consideration of process interactions. Part II is devoted to such unifying efforts, with four chapters (Chapters 10-13) covering four different endeavors: the unifying parameterizations based on assumed probability density functions; the EDMF approach that combines the Eddy Diffusivity and Mass Flux approaches to unify turbulence and convection; application of machine learning techniques; and innovative top-down attempts that consider the involved totality by borrowing ideas from systems theory, statistical physics, and non-linear sciences. Part III (Chapters 14-17) is devoted to assessments, model evaluation, and model-measurement integration, with four chapters that focus on satellite and airborne remote sensing measurements, surface-based remote sensing measurements, in-situ and laboratory measurements, and model evaluation, and model-measurement integration, respectively.

Biomass burning has shaped many of the ecosystems of the planet and for millennia humans have used it as a tool to manage the environment. When widespread fires occur, the health and daily lives of millions of people can be affected by the smoke, often at unhealthy to hazardous levels leading to a range of short-term and long-term health consequences such as respiratory issues, cardiovascular issues, and mortality. It is critical to adequately represent and include smoke and its consequences in atmospheric modeling systems to meet needs such as addressing the global climate carbon budget and informing and protecting the public during smoke episodes. Many scientific and technical challenges are associated with modeling the complex phenomenon of smoke. Variability in fire emissions estimates has an order of magnitude level of uncertainty, depending upon vegetation type, natural fuel heterogeneity, and fuel combustion processes. Quantifying fire emissions also vary from ground/vegetation-based methods to those based on remotely sensed fire radiative power data. These emission estimates are input into dispersion and air quality modeling systems, where their vertical allocation associated with plume rise, and temporal release parameterizations influence transport patterns, and, in turn affect chemical transformation and interaction with other sources. These processes lend another order of magnitude of variability to the downwind estimates of trace gases and aerosol concentrations. This chapter profiles many of the global and regional smoke prediction systems currently operational or quasi-operational in real time or near-real time. It is not an exhaustive list of systems, but rather is a profile of many of the systems in use to give examples of the creativity and complexity needed to simulate the phenomenon of smoke. This chapter, and the systems described, reflect the needs of different agencies and regions, where the various systems are tailored to the best available science to address challenges of a region. Smoke forecasting requirements range from warning and informing the public about potential smoke impacts to planning burn activities for hazard reduction or resource benefit. Different agencies also have different mandates, and the lines blur between the missions of quasi-operational organizations (e.g. research institutions) and agencies with operational mandates. The global smoke prediction systems are advanced, and many are self-organizing into a powerful ensemble, as discussed in section 2. Regional and national systems are being developed independently and are discussed in sections 3-5 for Europe (11 systems), North America (7 systems), and Australia (3 systems). Finally, the World Meteorological Organization (WMO) effort (section 6) is bringing together global and regional systems and building the Vegetation Fire and Smoke Pollution Advisory and Assessment Systems (VFSP-WAS) to support countries with smoke issues and who lack resources.

Convergent orogens are typically linear with laterally continuous, orogen-parallel folds and thrusts. Over the years, geoscience research has revealed evidence for important orthogonal/cross structures as well as lateral heterogeneity in deformation style, igneous activity, metamorphic grade, geomorphology, and seismic activity. To assess the occurrence, causal mechanisms, and implications of these lateral heterogeneities, a selection of convergent orogens, with different tectonic settings and history are reviewed. The Appalachians, the North American Cordillera, the Alps, the Himalayas, the Zagros, the Andes, and several other belts all exhibit a degree of lateral heterogeneity. Major factors driving the lateral heterogeneity and/or cross structures include the pre-existing deformational history of the cratonic blocks involved, lateral change in lithology of crustal rocks, variations in crustal/lithospheric rheologic properties, or changes in plate kinematics. The Appalachian orogenic front mimics the Iapetan rift margin. Pre-existing basement structures have control on pre- and syn-orogenic sedimentation, which subsequently impacts how an orogenic wedge evolves. A thicker sedimentary column generally evolves into a salient (as opposed to a recess), which is further enhanced by the presence of weak horizons as seen in the Zagros and the Cordillera. Lateral variation in sedimentary facies also creates changes in thrust-ramp geometry. During orogenic contraction, inherited basement structures can be preferentially reactivated based on their orientation. Several cross faults in the Himalayas spatially coincide with orogen-perpendicular, lower plate, basement structures. In a similar way, oceanic subducting plate physiography can also influence deformation in the overriding plate. Along-strike variations in subduction dynamics have been reflected in the Andean deformation. Orogenic extension in the Alps has been accompanied by a system of orogen-parallel strike slip faults and extensional cross faults. It is evident that lateral heterogeneities can form crucial control on the evolution of orogenic belts and can influence seismic rupture patterns, resource occurrence, and landslide-related natural hazards.