Earth9s Surface Research Articles

On carbon burial and net primary production through Earth's history

The carbonate carbon isotope record has been traditionally interpreted as evidence of stability in the globally integrated ratio of organic to total carbon burial from Earth9s surface environments over the past ∼3.8 billion years, but recent work has begun to question this conclusion. Herein, we use a reactive-transport modeling approach to track organic carbon oxidation at varying atmospheric oxygen levels and use that information to provide a rough estimate of net primary production through time. Our results support the emerging view that there was extensive variability in the fraction of carbon buried as organic matter (<i>f</i>_b,org) throughout Earth9s history. We strengthen the case that the carbonate carbon isotope record has been characterized by a relatively constant baseline value over time due to a fundamental mechanistic link between atmospheric O₂ levels and the carbon isotope composition of net inputs to the ocean-atmosphere system. Further, using estimates of the organic carbon burial flux (F_b,org) and the burial efficiency of the carbon pump from our marine reactive-transport modeling, we also support previous work suggesting extensive fluctuation in marine net primary production over time.

The role of the solid earth in regulating atmospheric O2 levels

Solid-earth processes act as both sources and sinks for atmospheric O₂. They act as sinks by introducing reduced minerals and gases to the earth9s surface that can remove O₂ from the atmosphere and ocean. They act as sources by exporting organic carbon and sedimentary pyrite to the mantle via subduction. Here we examine the relative sizes of igneous source and sinks of O₂ for the modern earth to determine their magnitudes and if they are in balance today. We find that igneous sinks for O₂ remove 1.83×10¹² mol O₂/yr (±0.43, 1σ) while subduction indirectly releases 1.56×10¹² mol/O₂ yr (±0.33, 1σ). This indicates that today igneous O₂ sinks are balanced by solid earth sources. We propose this balance is achieved by negative feedbacks associated with either low-temperature hydrothermal sinks for O₂, which are sensitive to deep-ocean O₂ concentrations, or the amount of organic carbon and pyrite buried in sediments and subducted, which are sensitive to dissolved O₂ concentrations. We also explore how igneous sinks for O₂ may have varied in the Neoproterozoic when atmospheric O₂ concentrations are thought to have been lower and the deep ocean anoxic. We find that despite these changes, the igneous O₂ sink was essentially the same as today: 1.78×10¹² (±0.43, 1σ) mol O₂/yr. We explore how this sink would change as the deep ocean accumulated sulfate, became oxygenated, and began oxidizing oceanic crust such that there was an increase in the subduction flux of oxidants to the subarc mantle. We propose that significant changes to the O₂ cycle, both in terms of positive and negative feedbacks could occur during these transitions. For example, accumulation of sulfate in the deep ocean would increase the oxidation state of high-temperature hydrothermal fluids, decreasing the size of this O₂ sink and thus promoting an increase in atmospheric O₂. In contrast, the oxygenation of the deep ocean would have allowed hydrothermally derived H₂S to react with and consume O₂ instead of being titrated out via reactions with dissolved Fe²⁺. Additionally, deep-ocean oxygenation would have initiated the oxidation of oceanic crust at low temperatures, creating new sinks for O₂. Finally, the oxidation of the subarc mantle via subduction of newly oxidized sediments and altered oceanic crust would have increased the oxygen fugacity of arc volcanic gases, decreasing their overall demand for O₂, allowing yet more O₂ to accumulate in the atmosphere. We place these changes into a conceptual framework and discuss their potential impact on the history of atmospheric and marine O₂ concentrations from the Neoproterozoic to late Paleozoic.

Rock weathering and nutrient cycling along an erodosequence

How flowing water and organisms can shape Earth9s surface, the Critical Zone, depends on how fast this layer is turned over by erosion. To quantify the dependence of rock weathering and the cycling of elements through ecosystems on erosion we have used existing and new metrics that quantify the partitioning and cycling of elements between rock, saprolite, soil, plants, and river dissolved and solid loads. We demonstrate their utility at three sites along a global transect of mountain landscapes that differ in erosion rates – an “erodosequence”. These sites are the Swiss Central Alps, a rapidly-eroding, post-glacial mountain belt; the Southern Sierra Nevada, USA, eroding at moderate rates; and the slowly-eroding tropical Highlands of Sri Lanka. The backbone of this analysis is an extensive data set of rock, saprolite, soil, water, and plant geochemical and isotopic data. This set of material properties is converted into process rates by using regolith production and weathering rates from cosmogenic nuclides and river loads, and estimates of biomass growth. Combined, these metrics allow us to derive elemental fluxes through regolith and vegetation. The main findings are: 1) the rates of weathering are set locally in regolith, and not by the rate at which entire landscapes erode; 2) the degree of weathering is mainly controlled by regolith residence time. This results in supply-limited weathering in Sri Lanka where weathering runs to completion in the regolith, and kinetically-limited weathering in the Alps and Sierra Nevada where soluble primary minerals persist; 3) these weathering characteristics are reflected in the sites9 ecosystem processes, namely in that nutritive elements are intensely recycled in the supply-limited setting, and directly taken up from soil and rock in the kinetically settings; 4) the weathering rates are not controlled by biomass growth; 5) at all sites we find a deficit in river solute export when compared to solute production in regolith, the extent of which differs between elements. Plant uptake followed by litter export might explain this deficit for biologically utilized elements of high solubility, and rare, high-discharge flushing events for colloidal-bound elements of low solubility. Our data and new metrics have begun to serve for calibrating metal isotope systems in the weathering zone, the isotope ratios of which depend on the flux partitioning between the compartments of the Critical Zone. We demonstrate this application in several isotope geochemical companion papers.

The role of vegetation in setting strontium stable isotope ratios in the Critical Zone

At Earth9s surface the stable isotope ratio of strontium (⁸⁸Sr/⁸⁶Sr) is predominantly set by biological uptake of Sr and its storage in plant litter. This conclusion was reached from a stable isotope mass balance that was independently validated by direct determination of elemental fluxes between the Critical Zone compartments (rock, soil, vegetation, and stream water) of three field sites located in the Swiss Alps, the US Sierra Nevada, and the tropical highlands of Sri Lanka. These sites cover a gradient in erosion rates, which is inversely related to the residence time of solids in the Critical Zone thereby constituting an “erodosequence”. For eroding landscapes, previous stable isotope models predicted that isotope ratios are set by the rate at which secondary solids form during the conversion of rock to regolith. Counter to this expectation we found that, after release from primary minerals, Sr is partitioned into one fraction taken up by plants and the remainder into dissolved Sr flux. The formation of secondary weathering products such as clays and oxides plays a subordinate role in determining the Sr budget. A Sr isotope fractionation factor for biological uptake was determined for each of the three ecosystems from the average Sr stable isotope composition in bulk plants and its dissolved counterpart in stream water. This fractionation factors range from <i>ca</i>. −0.3 ‰ for the Alps and Sierra Nevada to ∼0 ‰ for the tropical Sri Lanka site. That these isotope fingerprints caused by biologic uptake are preserved means that more Sr was physically removed in plant litter than recycled. Such Sr removal in plant litter appears to be strongest at the slowly-eroding site, whereas the dissolved Sr export by streams is highest at the site with the fastest erosion rate. There, all Sr taken up by plants is returned from litter back into solution. The site with short residence time of solids is the only one at which parent material and dissolved export differ in their Sr isotope composition. Our study shows that the behavior of Sr in the Critical Zone is in stark contrast to that of metals of which the isotope fractionation is not affected by biological uptake (for example lithium, mostly set by formation of secondary solids) or affected by both secondary solid formation and biological uptake (for example silicon). Strontium stable isotope signatures offer the new opportunity to quantify nutrient cycling in the Critical Zone as a function of environmental and ecological parameters.

NASA set to announce Earth system observatory

NASA is set to announce its next generation of Earth-observing satellites. As soon as this month, it will lay out plans for a multibillion-dollar set of missions that will launch later this decade. This Earth system observatory will offer insights into two long-standing wild cards of climate change—clouds and aerosols—while providing new details about the planet9s changing surface. The satellite fleets also mark a revival for NASA9s earth science, which has languished over the past decade compared with exploration of Mars and other planets. The satellite missions have been in planning for several years, but received a boost of interest from the Biden administration. The largest mission will involve multiple satellites in two different orbits, armed with radar and lasers capable of measuring clouds and atmospheric particles down to near Earth9s surface. Scientists hope the satellites will clarify how clouds could respond to global warming, while also delineating the degree that human pollution has altered clouds9 abundance. Other missions will use a hyperspectral imaging spectrometer—a molecular mapping system—and an infrared radiometer to measure the chemistry and changing heat of the planet9s surface, while a final mission will continue measurements of Earth9s changing gravitational distribution, allowing fine measurements of melting ice caps.

Constraints on surface temperature 3.4 billion years ago based on triple oxygen isotopes of cherts from the Barberton Greenstone Belt, South Africa, and the problem of sample selection

ABSTRACT Studies of Earth9s surface temperature before 3.0 Ga have focused heavily on the oxygen isotopic composition of silica-rich sedimentary rocks called cherts. Interpretation of the results have suggested early surface temperatures ranging from as high as 70 ± 15 °C down to those that differ little from modern values. A major controversy centers on whether differences in the oxygen isotopic compositions of cherts over time reflect changing surface temperatures, changing ocean isotopic composition, or post-depositional diagenetic and metamorphic effects. We here present results of triple oxygen measurements of 3.472 Ga to 3.239 Ga cherts from the Barberton Greenstone Belt, South Africa. The best preserved samples based on geological evidence have Δ917O and δ918O values that plot generally on or near the equilibrium fractionation line for silica precipitated out of modern, ice-free sea water. Geologic considerations allow many potentially useful samples to be eliminated for paleotemperature analysis because of proximity to younger mafic intrusions or interactions with meteoric waters during deposition, both of which tend to lower preserved isotopic values. Our results of triple-O isotopic analyses of a suite of samples representing deposition under open marine, shallow shelf conditions suggest that Archean surface temperatures were well above those of the present day, perhaps as high as 66 to 76 °C. They demonstrate that geologic context, including depositional setting and post-depositional history, requires careful assessment before the significance of oxygen isotopic results can be evaluated.

In search of blue.

New tools are aiding the age-old quest for the rarest of pigments.

Shallow water redox conditions of the mid-Proterozoic Muskwa Assemblage, British Columbia, Canada

The mid-Proterozoic was a time of apparent prolonged biological and geochemical stability, preceeding the environmental turmoil and rapid biological innovations that characterized the Neoproterozoic. Despite an upswing in work on the mid-Proterozoic over the past decade, basic aspects of the carbon cycle and Earth9s surface redox state during this time period remain poorly understood. To provide a new window into the mid-Proterozoic environmental evolution, we have investigated carbonates in the well-exposed Muskwa Assemblage located in NE British Columbia, Canada, for a combined stratigraphic and geochemical study. Rare Earth Elements and Yttrium (REE+Y) geochemistry was applied to carbonate rocks deposited over a marine paleoenvironmental depth gradient in order to characterize prevailing water column redox conditions. These data provide evidence for an extremely shallow chemocline with oxic surface waters being restricted to within storm-wave base, which is consistent with globally low oxygen in the ocean-atmosphere system. Furthermore, there is evidence for facies-dependent carbonate δ13C variability within the Muskwa Assemblage comparable in scale to typical stratigraphic variability recorded in carbonate strata of this age, highlighting the problems of using small carbon isotope excursions for chemostratigraphy.

The Maturity Myth In Sedimentology and Provenance Analysis

Abstract: We often resort to mythical thinking in the face of natural phenomena that we hardly understand. Sedimentary petrology has several long-standing myths. One is that sediments increase their “maturity” through time by winnowing and sorting, physical wear, chemical weathering, diagenesis, and recycling, as if their destiny were to reach a final stage of perfection represented by quartz spheres of equal size. Such an armchair representation of supermature purity is embodied in white recycled desert sand, whereas a modern analogue for its opposite, the dark dirty rock improperly called graywacke, is yet to be found. Clay matrix does not occur in sand deposited from tractive currents, which is sorted at the instant of settling. Sand grains get rounded relatively rapidly during transport in air but very slowly when transported in water. The degree of winnowing, sorting, and rounding (“textural maturity”) has little to do with the accumulation of “modifying energy” through time. “Mineralogical maturity” does not increase notably even after thousands of kilometers of transport in high-energy environments, and not even during recycling, a physical process that in a weathering-limited denudation regime tends at most to reproduce the mineralogy of parent clastic rocks. Rather, “mineralogical maturity” decreases drastically where sedimentary rock fragments are eroded in abundance from mudrocks interbedded in the source, and sand recycled entirely from orogenic flysch or molasse may contain less than 10% quartz. If natural sediment factories were quartz distilleries, then quartzose sand should become more common through geological time. Pure quartz sand, however, is relatively rare in the modern world, and largely confined to hyperhumid equatorial latitudes or recycled eolian dunefields. A relative increase in more durable minerals is achieved effectively only by chemical processes such as selective leaching in soils, or especially during burial diagenesis, when the time and temperature available for chemical reactions are much longer and higher than at the Earth9s surface. If recycled sediments are commonly quartz-rich with very poor assemblages dominated by zircon, tourmaline, and rutile, it is because their parent sandstones have undergone diagenetic dissolution prolonged for many millions of years at temperatures of many tens of degrees before final exhumation and erosion.

Microstructural preservation and the effects of diagenesis on the carbon and oxygen isotope composition of Late Cretaceous aragonitic mollusks from the Gulf Coastal Plain and the Western Interior Seaway

The carbon and oxygen isotope compositions of calcium carbonate shells are widely accepted and applied proxies for tracking changes in paleoenvironmental conditions such as temperature, salinity and productivity. In order to accurately interpret isotopic measurements, diagenetic alteration must first be assessed. The occurrence of aragonitic shells is often taken as a first order sign of unaltered material because aragonite at the Earth9s surface is metastable and converts to calcite. However, even specimens that retain an aragonitic composition and are macroscopically well preserved often exhibit subtle to considerable signs of alteration when shell microstructure is examined using scanning electron microscopy (SEM). To determine the textural and isotopic effects of progressive alteration on differing types of shell microstructure, we undertook a comparative study of aragonitic shells from two regions frequently used in paleoenvironmental reconstructions and diagenetic studies -- the Upper Cretaceous of the Gulf Coastal Plain (GCP) and the Western Interior Seaway (WIS). Because the GCP is within a passive margin setting and the WIS has experienced tectonic processes, we also evaluate how diagenetic history affects isotopic composition. Visually well-preserved ammonite, bivalve, and gastropod shells were collected from one locality in the GCP and examined using SEM. To evaluate microstructural preservation, we used a previously published scale based on WIS specimens for nacreous shell material and a complementary scale we developed for crossed lamellar microstructure. The stable carbon and oxygen isotope compositions of specimens across the preservational scale from both regions were analyzed. Isotopic composition does not change systematically with degrading preservation in the GCP specimens, a result that contrasts strongly with patterns in WIS specimens where isotopic composition systematically decreases with decreasing microstructural preservation. Dissimilar tectonic regimes that led to unique post-depositional conditions for each region are invoked to explain this difference. The WIS was a foreland basin subjected to significant meteoritic groundwater flow driven by active uplift, while the GCP was a passive margin that has remained close to sea level, with low hydraulic potential, since the time of deposition. Thus, during diagenesis the WIS shells were exposed to fluids that differed greatly from the seawater in which the organisms grew, whereas diagenetic fluids in GCP settings likely were similar to marine waters. As expected, shells with the best-preserved microstructure provide the most consistently reliable isotopic data for paleoenvironmental reconstructions, but our comparisons show that similar degrees of microstructural alteration can express very different diagenetic shifts in isotopic values.

Geochemical Tracers of Extraterrestrial Matter in Sediments

Every year, tens of thousands of tons of cosmic dust accumulate at the Earth9s surface, representing a continuation of the accretion process that started 4.57 billion years ago. The unique geochemical properties of these materials, compared to the Earth9s surface, render them excellent tracers of Solar System, atmospheric, oceanographic, and geologic processes. These processes can be recovered from the records preserved in marine and terrestrial sediments, including snow and ice. We review evidence from these natural archives to illuminate temporal and spatial variations in the flux and composition of extraterrestrial material to Earth, as well as the terrestrial processes that affect the distribution of extraterrestrial tracers in sediments.

Supergene Alteration of Ore Deposits: From Nature to Humans

Supergene minerals form under near-ambient conditions on the Earth9s surface. Supergene mineralization is controlled by the parent rock composition, climatic conditions, geomorphological environment, and chemical compounds added during mineral processing. They appear in alteration zones called “orecretes.” Bronze Age miners exploited these easily accessible high-grade soft ores for Fe, Cu, Pb, and Ag. Some supergene minerals can also grow in poorly ventilated mining galleries and shafts, coat metal mining artifacts and smelting residues, and form from disastrous blasts and fires in ancient mining settlements. Supergene deposits bridge the gap between humans and metal resources at the interface between rock, soil, air, water, and living organisms. These deposits provide essential clues to geological, environmental, and archeological studies.

Tracing and Pacing Soil Across Slopes

The conversion of rock to soil prepares Earth9s surface for erosion by wind, water, gravity, and life. Together these agents wear down hills and mountains even as the land rises up under the stress of tectonic forces in the crust. Meanwhile, weathering liberates nutrients from minerals and disaggregates rock into regolith, generating hospitable substrates for life. Over the last two decades, geochemists, geomorphologists, and soil scientists have increasingly used cosmogenic nuclides to quantify how fast soils are made, modified, and finally swept away in hilly and mountainous landscapes around the world. These studies are revolutionizing our understanding of soils and their role in feedbacks that shape Earth9s surface, influence overlying ecosystems, and modulate climate over millions of years.

Applications of airborne and terrestrial laser scanning to paleoseismology

Paleoseismic investigations aim to document past earthquake characteristics such as rupture location, frequency, distribution of slip, and ground shaking intensity—critical parameters for improved understanding of earthquake processes and refined earthquake forecasts. These investigations increasingly rely on high-resolution ( 2 /m. This situation refines interpretations of PBR exhumation rates and thus their effectiveness as paleoseismometers. Given that earthquakes disrupt Earth9s surface at centimeter to meter scales and that depositional and erosional responses typically operate on similar scales, ALS and TLS provide the absolute measurement capability sufficient to characterize these changes in challenging geometric arrangements, and thus demonstrate their value as effective analytical tools in paleoseismology.

Distal Impact Ejecta Layers: Spherules and More

During the formation of large impact structures, layers of melted and crushed rock (ejecta) are deposited over large areas of the Earth9s surface. Ejecta thrown farther than 2.5 crater diameters are called distal ejecta. At distances greater than ~10 crater diameters, the distal ejecta layers consist primarily of millimeter-scale glassy bodies (impact spherules) that form from melt and vapor-condensate droplets. At least 28 distal ejecta layers have been identified. Distal ejecta layers can be used to place constraints on cratering models, help fill gaps in the cratering record, and provide direct correlation between impacts and other terrestrial events.

Tourmaline: A Geologic DVD

Tourmaline is an eye-catching mineral, but even more importantly, it has played a significant role in the evolution of scientific thought and, more recently, has been recognized as a medium for recording geologic information, not unlike a DVD. With its plethora of chemical constituents, its wide range of stability from conditions near the Earth9s surface to the pressures and temperatures of the upper mantle, and its extremely low rates of volume diffusion, tourmaline can acquire a chemical signature from the rock in which it develops and can retain that signature through geologic time. As a source as well as a sink for boron, tourmaline is nature9s boron recorder. Tourmaline can be used as a geothermometer, provenance indicator, fluid-composition recorder, and geochronometer. Although long prized as a gemstone, tourmaline is clearly more than meets the eye.

Lawsonite vorticity and subduction kinematics

The exceptional preservation of lawsonite in eclogite and blueschist in a subduction complex (Sivrihisar, Turkey) allows evaluation of high-pressure (H P ) deformation and exhumation using vorticity analysis of a H P index mineral. The Sivrihisar H P rocks were deformed during H P metamorphism and initial decompression by oblique (normal and/or dextral) shearing beneath serpentinized peridotite. We evaluated kinematic vorticity (W m pure shear = 0, W m simple shear = 1) using the shape fabric of lawsonite crystals in blueschist layers and meter-scale eclogite pods. Pods record dominant simple shear (W m > 0.8) in their eclogitic core and at pod margins partially transformed to blueschist; map-scale blueschist layers record a large component of pure shear (W m = 0.4–0.6), consistent with oblique extrusion at depth in the subduction zone, and local simple shear (W m = 0.8) at the fault contact with serpentinite. A combination of oblique unroofing from beneath a weak serpentinized hanging wall and pure shear extrusion in the subduction channel accounts for rapid exhumation along a low geothermal gradient and the rare preservation of lawsonite eclogite during exhumation to the Earth9s surface.

Time Scales of Metamorphism, Deformation, and Crustal Melting in a Continental Arc, North Cascades USA

The record of metamorphism, deformation, and melting in the North Cascades continental arc provides insights into the timing and mechanisms of extensional unroofing that followed crustal thickening. The Skagit Gneiss (North Cascades) is composed of variably deformed 90–45 Ma tonalitic to granitic intrusive rocks. These lithologies and metasedimentary rocks are migmatitic. Zircon and monazite from different textural varieties of migmatite from three outcrops along an east-west transect were analyzed using the isotope dilution–thermal ionization mass spectrometry (ID-TIMS) technique. The data reveal two main migmatization pulses: (1) 68–63 Ma and (2) 53–47 Ma. In the westernmost locality, leucosome zircon yields group 1 dates, and mesosome (sillimanite-garnet-biotite gneiss) zircon is as young as 61 Ma. Leucosome zircon in the easternmost outcrop yields only group 2 dates, and biotite gneiss contains 47 Ma zircon. The third outcrop has leucosome dates from both groups: 65 Ma and 53 Ma. Monazite from leucosomes and mesosomes likely records the timing of prograde metamorphism (ca. 69 Ma) and later synkinematic ± fluid-mediated growth (49–46 Ma). These results indicate that partial melting occurred during 71–61 Ma metamorphism and lasted through 46 Ma deformation associated with exhumation. The results and field observations suggest the presence of ductilely deforming crust from 68 to 46 Ma. The similarity between the youngest U-Pb dates in the migmatites and cooling and basin-filling ages suggests a link between ductile and brittle processes over a range of structural levels in the arc, from a zone of crustal melting, flow, and migmatite crystallization to Earth9s surface.

High-resolution spatial rupture pattern of a multiphase flower structure, Rex Hills, Nevada: New insights on scarp evolution in complex topography based on 3-D laser scanning

Fault scarps represent the most obvious expression of tectonic activity at the Earth9s surface. Studies on scarp morphology place constraints on fault kinematics and scarp-degradation processes, and were often based on geomorphic dating techniques. Fault scarps exposed in areas of simple topography facilitate data acquisition and interpretation, whereas little work had been done where fault scarps are superimposed on complex, dissected topography. Fault scarps developed in complex topography are commonly observed along flower structures and at tips of strike-slip faults. Such structures are important elements for evaluating the evolution and linking of strike-slip fault systems, and appear to be scale-independent from several meters to hundreds of kilometers. We examined the detailed meter- to hundred meter–scale structure and surface expression of a flank of one fault scarp–bounded pressure ridge (Rex Hills flower structure) by combining field mapping with high-resolution digital elevation model (DEM) analysis. Based on terrestrial laser scanning we generated a detailed DEM and extracted high-resolution topographic cross sections, which enabled us to identify fault scarps and to determine their relative ages and geometry. Our study site is located on the transpressional left-bend between the Pahrump and Amargosa segments of the dextral Stateline fault system. The topography is characterized by alternating valleys and ridges (each ∼100 m long, relief of ∼4 m). We observed the following: the southern Rex Hills slope exhibits three fault scarps related to three reverse fault branches; the basal scarp (scarp 1) is most continuous, and exhibits five segments, the upper two scarps (scarps 2 and 3) are less continuous. Furthermore, fault scarps exposed on ridge crests are more numerous (up to four to five scarps), and smaller (∼5 m high); valleys often exhibit single large (>10 m high), smoothed scarps. To easily detect differences between the scarps, we evaluated the height and slope angle of the scarps using topographic cross sections. Our analysis indicates that scarp shape is influenced by fault dip, lithology, and degradation processes resulting in large scatter and broad overlap in scarp-height–slope-angle space. The analysis further indicates that scarp degradation is stronger in the valleys, and that the preservation potential of small, individual fault scarps is therefore greater on the ridge crests. We compared our fault-scarp data with published, calibrated data yielding an age of ∼2 ka for the Rex Hills scarps consistent with an earlier finding. This suggests that the scarp shape mainly reflects progressive degradation since the most recent surface rupture. Our approach of analyzing high-resolution topographic data of closely spaced fault scarps is promising especially when combined with subsurface data as well as geochronological and paleoseismic data, and it provides a basic scheme for analyzing scarp populations in a complex topographic region. Despite the absence of subsurface data, our approach allowed the study of complex high-resolution fault-scarp morphologies across a flower structure for the first time.

New Criteria for an Intensity Scale in Iran and Surrounding Countries

This paper introduces innovative criteria for evaluating earthquake intensity in Iran and surrounding countries. Two characteristics of the region make it necessary to develop such criteria: 1) the special properties of buildings and other structures in the region; and 2) the cultural and environmental characteristics of Iran and its neighbors. The proposed criteria are compatible with the international intensity scale in that there are 12 different descriptions for 12 intensity levels ranging from very weak (level I) to strongly destructive (level XII). The criteria are based mainly on observed earthquake effects, including damage to buildings, other structures, and furniture, and changes in environmental conditions including cracks in the Earth9s surface, changes in water flow, and so forth.