A magnetic field measurement suite intended for CubeSat and ground-based geomagnetic applications is presented. The system is composed of commercial-off-the-shelf sensors (COTS), which include four PNI RM3100 magnetometers, a Bosch BMI270 inertial measurement unit (IMU), and a TMP36 thermal sensor. The instruments are collectively operated by a Texas Instrument’s MSP430FR5949 microcontroller. The novel measurement principle employed by the magnetometers permits a low fabrication cost, power consumption, and footprint; in turn, this enables the incorporation of four magnetometers (theoretically many more), reducing the magnetic noise floor and increasing the resolution by a factor of two in this case. Additionally, the inclusion of a COTS IMU allows us to reliably establish the orientation of the sensor package, thus permitting a better understanding of the geometry of the surrounding magnetic field under static or dynamic conditions. The system has been tested and characterized in a controlled laboratory environment with the intent of flying aboard the PR-CuNaR2 CubeSat, set to launch early next year. This mission will raise the technology readiness level (TRL) of the system (current TRL is approximately 4/5) and provide us with valuable measurements of the magnetic environment at Low-Earth-Orbit.

Wildfires are one of the main sources of disturbance in boreal forests. Post-fire changes to soil temperature and moisture regimes can have wide-ranging impacts on boreal forests including the depth at which permafrost is found, vegetation recovery, and carbon and nitrogen cycling. Surface soil temperatures increase following fire, due to loss of shading from tree canopies and a thinner surface organic layer. Post-fire soil temperature and moisture regimes also change due to reduced transpiration and changes in surface albedo. The duration of these changes depends on factors such as region, fire intensity, and soil texture. Here we present results from a long-term (1999 to present) dataset of soil conditions for four black spruce boreal forest sites located in Interior Alaska across burn and permafrost gradients: 1) burned, no permafrost, 2) unburned, no permafrost, 3) burned, with permafrost, and 4) unburned, with permafrost. The data from these sites demonstrate how both burning and the presence of permafrost influence soil temperature and moisture, as well as the timing of seasonal changes, for over twenty years. In addition, we discuss the challenges of maintaining and collecting data from field instruments deployed for decades in harsh conditions. All data discussed in this presentation will be available on the Bonanza Creek Long-term Ecological Research (LTER) website and is available for future studies.

Tropical cyclones dominate the disturbance regime experienced by forest ecosystems in many parts of the world. Interactions between cyclone disturbance regimes and nutrient availability strongly influence forest ecosystem dynamics. However, uncertainty exists over the importance of soil fertility properties (i.e., total soil phosphorus-P concentration) in mediating forest resistance and recovery from cyclone disturbance. We hypothesized that forests on soils with low total P (e.g., developed on limited-P parent material) have a higher resistance to but a slower recovery from cyclone disturbance than forests on high P soils. We investigated cyclone impacts on litterfall, an essential conduit for nutrient recycling in forest ecosystems. We compiled site-level forest litterfall data from 53 studies and datasets associated with 15 naturally-occurring one simulated tropical cyclone in 23 sites within five regions (Taiwan, Australia, Mexico, Hawaii, and the Caribbean)and four cyclone basins. We calculated the effect sizes of cyclone disturbance on the litterfall mass and nutrient (P and nitrogen-N) concentrations and fluxes during the first (< five) years post-disturbance across a total soil P gradient. We also assessed the effect of 20 covariates on the degree of cyclone impact on litterfall. Total litterfall mass flux increased by 4820%following cyclone disturbance. Such an initial increase in litterfall mass reflects the magnitude of cyclone-derived plant material input to the forest floor, which was highest in the Caribbean and lowest in Taiwan. Among 20 covariates, soil P and region were the best predictors of cyclone effects on total litterfall mass, explaining 80% of the variance. The effect sizes increased linearly with soil P and region, from significantly lower in Taiwan (low-P) to largest in the Caribbean (high-P). Total litterfall P and N fluxes increased significantly post-cyclone, whereas the increase in leaf P flux was twice as that in Nflux. Results highlight the importance of understanding the interactions between disturbance and nutrient gradients in forest ecosystems to understand forest responses to altered cyclone regimes expected under climate change.

GOSAT and GOSAT-2 have simultaneously observed both reflected SWIR solar light and TIR emissions with a single FTS mechanism with the Thermal And Near-infrared Sensor for carbon Observation Fourier-Transform Spectrometer (TANSO-FTS) and TANSO-FTS-2 since 2009 and 2018, respectively. Their linear polarization bands provide information on light-path modification and make accurate remote sensing possible, even under aerosol and thin-cloud contaminated conditions. We can retrieve the difference between the partial column-averaged dry-air mole fractions of the two individual layers of lower and upper troposphere (LT and UT) by combining TIR and SWIR spectra data simultaneously, thereby constraining the accurate total column density of XCO2 and XCH4. TANSO-FTS has a two-axis agile pointing system, which allows cross-track and along-track motions It was originally designed for grid scan observations and viewing onboard calibration sources. After the pointing mechanism was switched from primary to secondary on 26 January 2015, We decided to make more frequent target observations, by uploading AT and CT pointing angles and observation timing as commands from the ground every day About 1000 locations are allocated to target observations such as calibration and validation site, megacities, or large emission sources. We define vertical layers of LT and UT not by temperature, but by the retrieved Psurf from individual O2 A band data. The pressure-height ranges of the LT and UT were taken as 0.6–1 Psurf and 0.2–0.6 Psurf, respectively. As the LT includes the entire boundary layer, analysis using XCO2 (LT) and XCH4 (LT) can double the signal of local emissions and remove the effects of CO2 and CH4 variability in the UT, which typically extends over a much wider area. We have targeted intense measurements over mega cities since 2016. We assume the average density of the upper troposphere is a background. We define XCO2 anomalies XCO2(LT)-XCO2(UT average), which show enhancement caused by local anthropogenic emissions. In 2020, we detected lower anomalies than previous years over mega cities such as Tokyo, Beijing, and New York.

Years of the Maritime Continent or YMC was designed to improve our knowledge of the weather-climate systems over the MC and their numerical simulation and prediction skill. Since its first field campaign in November 2017, many intensive observations have been carried out under the coordination with the MC countries. Although currently some observations have been postponed due to COVID-19 pandemic, field campaigns are expected to continue beyond 2021. Up to now, some key information could be obtained, which suggest future approaches. In particular, diurnal cycle of rain near the coast is one of major targets, as they are dominant component of precipitation in this region. Some studies suggest the important role of temperature contrast between land and ocean, and inaccurate initial sea surface temperature conditions might cause a delay of offshore propagation of rainfall region. This fact provides a clue to improve simulation of precipitation behavior over the MC. In addition, during the campaign, several new observation tools have been introduced. For example, autonomous surface vehicle (ASV) had been deployed and measured surface meteorology as well as sea surface condition. Besides, GNSS-derived water vapor measurement was successfully carried out. Those results suggest that such ASVs equipped with new tools can be used to monitor accurate sea surface condition without significant cost and time. However, usually those instruments are not allowed to operate freely in the MC. Thus, based on collaboration with the MC countries, researchers in the MC are highly expected to take this role as regional representative. In this presentation, we will also show other results which provide tips for future direction.

Submarine slope failures and the tsunamis they generate pose risks to coastal communities and infrastructure. While slope failures on passive margins represent some of the largest mass failures on Earth, little is known about their dynamics. The recurrence interval of submarine slope failures on passive margins is longer than on active margins, which facilitates thick sediment accumulation before failure, yields larger failures, and may be associated with higher potential for tsunami generation. While numerous studies model failure likelihood based on temporal distribution, overpressure, or earthquake proximity, there is limited insight linking initial conditions, preconditioning, slope failure initiation, and failure evolution. We observed dynamic submarine slope failure processes via physical experiments in a benchtop flume. Submarine slope failures were induced under controlled pore pressure with varied sand-clay mixtures (0%, 2%, 4%, and 5%, clay, by weight) constrained to a constant pre-failure slope geometry. Commercially obtained fine-grained sand (subangular quartz; 87% SiO2; D50 = 195 µm) and clay (dioctahedral smectite; 63% SiO2 and 21% Al2O3; D90 = 44 µm) were used. Pore pressure required to induce slope failure, slope-failure initiation and evolution, and post-failure morphology were recorded and analysed via photogrammetry. Numerical models were developed to quantify the physical processes observed in flume experiments. Increased clay content corresponded to increased cohesion and pore pressure required for failure. Subsurface fractures and tensile cracks were only generated in experiments containing clay. Falling head tests showed a log-linear relation between hydraulic conductivity and clay content which we used in our numerical models. Models of our experiments effectively simulate overpressure (pressure in excess of hydrostatic) and failure potential for (non)cohesive sediment mixtures. Overall our work shows the importance of clay in reducing permeability and increasing cohesion to create different failure modes due to overpressure. Ongoing work is investigating the effects of higher clay content and the role of seismic energy in slope failure morphology.

Representation of canopy and tree function in earth system models (ESMs) is going through rapid advancements in the last decade. The simplistic big-leaf representation of canopy in model is being expanded and replaced by more complex canopy representations that include multiple functional types, species and age/size stages, multiple patches with different canopy height and leaf area characteristics, and vertically detailed representations with between 2 (light and shade) to n canopy leaf layers. Recently, the hydrodynamic approach to modeling stomata conductance has advanced, and many ESMs include a hydrodynamic version. Under the hydrodynamic approach, stomata respond to water availability in the xylem, and not directly in the soil. The result is a model that include the stem, and xylem dimensions as canopy characteristics for determining the flow and storage of water in the xylem. However, pipe diameter, area and volume do not scale linearly, and thus, the simulations cannot resolve canopy-scale hydrodynamics by pulling all the stem conductive area and volume to a single virtual patch scale, but instead, need to consider the hydrodynamics of a single virtual tree and scale its resulting fluxes to the entire canopy. While that is trivial in a homogeneous canopy, the difference between the tree-level description of the hydrodynamic canopy and the horizontally pulled description of the canopy in the surface-flux and radiation-exchange modules leads to a conundrum. Imagine a mixed canopy: 50% oaks and 50% maples. Assume oaks have 20% more LAI and are 1 m taller than the maples. As far as hydrodynamics are concerned, the evaporative demands of maple follow from light attenuation and leaf area profiles of a maple-like canopy. However the roughness length and aerodynamic resistance, and the resulting wind profile inside the canopy is not characteristic of maple or oak but is a result of the mixed canopy. I will present formulation for a consistent scaling of tree-level canopies to patch-level for mixed forests with multiple species of different functional types. The formulation scales canopy characteristics and the resulting canopy fluxes from tree to forest in an energy and mass-conservative way, and allow a smooth and consistent multi-species canopy description for hydrodynamic models in mixed-forests.

The retroarc of the North American Cordilleran orogen in Nevada and Utah has been divided into the frontal Sevier fold-thrust belt in Utah, which accommodated shortening between ~145 and ~50 Ma, and a broad region of Nevada referred to as the ‘Sevier hinterland’. The hinterland is hypothesized to have developed into a high-elevation orogenic plateau (or ‘Nevadaplano’) at some point between the Late Jurassic and the Paleogene. Recent paleoaltimetry utilizing clumped isotope temperature estimates suggests that at least some basins on the Nevadaplano were at an elevation of 2.2-3.1 km by the latest Cretaceous. However, it remains uncertain precisely when the Nevadaplano attained these high elevations and if surface uplift developed steadily along with protracted shortening in the Sevier fold-thrust belt or occurred rapidly and was decoupled from the shortening record. In order to extend the surface elevation history of the Nevadaplano further back in time, we have investigated the type-exposure of the mid-Cretaceous (~113-98 Ma) Newark Canyon Formation (Knc) in central Nevada. The Knc records synorogenic sedimentation in the Sevier hinterland during the early to middle stages of shortening in the Sevier thrust belt. We will present terrestrial surface temperature estimates from clumped isotope analyses derived from palustrine, lacustrine, and pedogenic carbonate-bearing facies. Contextualized by structural evidence and corrected for secular climate change, these data suggest that the studied Knc basin had not developed substantial surface elevation by the mid-Cretaceous. However, there was likely some considerable surface relief in this region associated with active fold-thrust structures in the upper crust. Preliminary temperature estimates range between 22 and 70°C. These temperatures reflect a range of facies-specific differences in primary carbonate formation, as well as, diagenetic overprinting of some samples. Consistently warm temperatures throughout the stratigraphic section suggest that there was no significant cooling due to elevation gain between ~113 and ~98 Ma. We will discuss the implications of these results for the style and timing of deformation and surface uplift within the Nevadaplano.

Disabled scientists are severely underrepresented in geosciences, including paleo-related fields. In this presentation, I will explain how potential benefits from remote work can help improve access for disabled scientists (broadly defined). Some improvements include fewer barriers due to commuting to work (which contributes to fatigue) or physical access to buildings and labs, reduced stimuli (potentially helpful for learning disabilities and migraines), and more flexible working hours (helpful for a range of disabilities). Although restricted access to labs may change research directions, it’s possible for some computational research to continue. However, there are also new challenges arising from remote work, from social isolation to non-ideal work environments, that may have a disproportionate impact on disabled researchers. The pandemic has also forced some researchers to disclose their health conditions to explain that they are at a high risk for severe illness from COVID-19. I suggest that, even after COVID-19 is resolved, the paleo communities continue to support flexible work options, which could improve the representation of disabled scientists. Furthermore, we can use this period of reduced fieldwork and remote teaching to consider how to improve access for all scientists at field sites, in classrooms, and in labs.

Synthetic aperture radar (SAR) multi-temporal techniques have been proposed to improve image resolution, persistent-scatterer detection, and damage-map generation (Bujor et al., 2004; Hooper, 2008; Yun et al., 2012). The usage of multiple scenes diminishes the speckle noise commonly present in a SAR image and increases the overall signal-to-noise ratio (SNR) of dominant radar scatterers. Following the same idea, we propose a new SAR processing workflow based on the back-projection algorithm (Cafforio et al., 1991). We employ the back-projection method’s flexibility to focus the radar pulses at multiple depths shifted with respect to the reference digital elevation model (DEM), yielding a volume of SLCs discretely sampled over a range of elevations/depths. These scenes are then combined to produce a single-look complex (SLC) image, which presents increased SNR and effective resolution. Similar image improvements can be achieved by spatially averaging a SLC image generated at high spatial sampling. However, the proposed method requires a fraction of the processing time of the fine-spatial SLC formation. The proposed approach retains the same benefits of any back-projection algorithm and enables the formation of SLC images corresponding to large Earth surface extents.

Solar-Induced chlorophyll Fluorescence (SIF) provides a powerful proxy for determining forest gross primary production (GPP), particularly in evergreen ecosystems where traditional measures of greenness fail. The dynamics of the SIF/GPP relationship, however, are poorly understood under varying viewing directions and light conditions. This is, in large part, due to challenges in measuring SIF at the spatiotemporal scale that is necessary to understand these effects. Therefore, the aim of this work is to utilize high-temporal and spatial resolution SIF measurements to better constrain the response of SIF to ambient canopy illumination and viewing geometry. We use a PhotoSpec instrument and eddy covariance measurements to explore the SIF/GPP relationship under various viewing directions and light conditions during the 2019 and 2020 growing seasons at the Old Black Spruce site in Saskatchewan, Canada. PhotoSpec is a tower-based 2-D scanning spectrometer system capable of taking Fraunhofer-line based SIF retrievals in the red and far-red wavelength ranges with a 0.7 degree field of view at a ~30 second time resolution. Measured SIF and GPP are combined with SCOPE modelling results to provide a mechanistic understanding of the physical and ecophysiological drivers for the SIF/GPP relationship in the Boreal Forest. Our results show that viewing direction and solar zenith/azimuth angles are important for the SIF signal under direct light conditions, but not under diffuse. Furthermore, the SIF/GPP relationship changes under direct and diffuse light conditions at a 30 minute, daily, and monthly resolution. Our ability to use SIF as a proxy for GPP depends on a quantitative understanding of radiative transfer within the canopy and how scanning geometry impacts SIF measurements. These results provide an important insight into these relationships in the Boreal forest, a region where GPP has been traditionally difficult to track using remote sensing.

High altitude platforms (HAPs) such as stratospheric balloons and eventually other high altitude, long endurance unmanned vehicles have reached a stage where it is possible to deploy a persistent fleet of aircraft acting as a meteorological observation network for a reasonable cost. Whether directly collecting in situ measurements like winds aloft or via dropsondes or performing remote sensing using, for example, radar or GPS radio occultation, these observation networks can collect measurements which are hard to obtain from other observation platforms and are complementary to other systems. They are also highly autonomous and can be deployed worldwide (and thus can add redundancy to the global forecast system). Because they are mobile, the observation network can be adjusted to collect in situ measurements in the places that are most important to forecasters and scientists. We use simulation of fleets of stratospheric balloons that are navigated by machine learning algorithms that actuate an altitude control system to demonstrate some of the potential constellations that are achievable with HAPs and motivate the greater consideration of an autonomous, persistent HAPs-based meteorological observing network.

The development of thermodynamic modeling techniques and availability of updated thermodynamic databases and activity-composition (a-X) relations, call for an evaluation of modeling pressure-temperature (P-T) paths of metabasites. In this study, eclogite from the Tso Morari UHP terrane, NW India, is used as a representative metabasite to compare P-T paths generated from the widely used THERMOCALC (TC) and Theriak-Domino (TD) programs. We also evaluate the effect of using the most updated thermodynamic database ds 62 (Holland and Powell 2011) relative to an older version ds 55 (Holland and Powell 1998), and the most updated garnet a-X relations of White et al. (2014) (W14) relative to an older version of White et al. (2007) (W07), while accounting for the effect of garnet fractionation. The following modeling protocols were assessed: (1) TC33: TC v3.33 with ds 55 and garnet a-X relations of W07; (2) TC47: TC v3.47 with ds 62 and garnet of W14; (3) TDG: TD with ds 62 and garnet of W14, and (4) TDW: TD with ds 62 and garnet of W07. TC47 and TDG modeling protocols yield a similar peak metamorphic P-T of 34 ± 1.5 kbar at 544 ± 15 °C and 551 ± 12 °C, respectively; while TC33 and TDW modeling yield similar peak P-T results: 26 ± 1 kbar at 565 ± 8 °C and 28.5 ± 1.5 kbar at 563 ± 13 °C, respectively. Results indicate that all four modeling protocols generally provide consistent thermodynamic simulations regarding metamorphic compositional and temperature evolution; however, the pressure generated by protocols using W14 (TC47 and TDG) is 5–8 kbar higher than that predicted by protocols using W07 (TC33 and TDW). The difference in peak pressure results for the modeling protocols (TC47 and TDG vs. TC33 and TDW) are beyond the suggested uncertainty using mineral isopleth thermobarometry in pseudosections: ± 50 °C and ± 1 kbar at 2σ (Powell and Holland 2008). This study illustrates that the choice of garnet a-X relations can affect predictions of peak pressure regardless of program choice, as well as the need of comparison between modeling predictions and petrological observations.

Seismic-frequency torsional forced-oscillation measurements of shear modulus dispersion and associated strain-energy dissipation under conditions of simultaneously high temperature and pressure in our laboratory require the specimen to be enclosed within a thin-walled metal sleeve – typically of mild steel. However, the well-known transition between the austenite and ferrite phases on cooling across the interval 900-700ºC complicates its mechanical behaviour. The resulting uncertainty tends to mask the seismologically important onset, within this temperature range, of appreciably anelastic behaviour of polycrystalline olivine. In order to more closely document this important transition in mechanical behaviour, we have conducted an unpublished study in which of a specimen of polycrystalline olivine is jacketed within a copper sleeve which retains its face-centred-cubic (fcc) structure throughout the range of the measurements limited to 1050ºC by the proximity of the melting point. Here we report measurements to higher temperature (1200ºC) in which we employ austenitic (fcc) stainless steel (SS) as an alternative jacket material. Two parallel reference experiments with a SS-jacketed SS specimen and a SS-jacketed sapphire specimen were also conducted to obtain the mechanical properties of the jacket material. Such information concerning the viscoelastic behaviour of SS is used to subtract the torsional stiffness of the SS jacket from the properties of SS-jacketed olivine and thereby isolate the mechanical behaviour of olivine. The resulting dissipation spectrum for the olivine specimen consists of a monotonic background dissipation with a superimposed peak located within the 1-1000 s period range for temperatures between 900 and 1050ºC. The dissipation peak and associated shear modulus dispersion, potentially attributable to elastically accommodated grain boundary sliding, display an Arrhenius dependence upon temperature - moving systematically to shorter periods with increasing temperature. Comparison of the results obtained for sol-gel Fo90 olivine specimens enclosed within the alternative mild-steel, copper, and stainless-steel jackets will provide new insight into the nature of the seismologically important transition between the elastic and anelastic regimes.

Increases in soil organic carbon (SOC) during secondary succession in Mediterranean and semi-arid climates, global hot-spots for agricultural land abandonment, have been notoriously difficult to predict and are subject to multiple environmental and land management factors. Field studies have reported positive, negative and no change varying over extended periods of time. To better evaluate the potential carbon sink capacity of regenerating semi-natural landscapes in these climates requires an improved understanding of the rates of SOC gains and losses. We compiled Mediterranean and semi-arid chronosequences and paired plots to investigate the effects of past land use, restoration intensity, and various environmental factors on SOC stocks during post-agricultural succession. Based on a preliminary synthesis of the western Mediterranean basin, we expect significant long-term accumulation rates globally although with high variability and the potential for net losses (compared to cropland control sites) even after several decades. Losses or minimal change are likely due to high initial SOC stock at the time of abandonment (e.g. from anthropogenic organic matter inputs) and too high or too low mean annual precipitation (e.g. < 450 or > 1000 mm), among other factors. A consolidated SOC accumulation rate for both Mediterranean and semi-arid soils undergoing post-agricultural succession is provided to better inform decision-makers on the benefits and challenges of agricultural land abandonment.

The SW Portuguese margin has been intensively studied, particularly for rifting, tectonic inversion and tectonic reactivation of the Atlantic passive margin. In this work we bring new data on the continental shelf, usually not acquired by the heavier geophysical methods (e.g. airborne or low resolution deep seismic-magnetic surveys). These new data allow casting a clear light bridging between the geological structures onshore and offshore. The geology of this margin went through the Variscan orogeny of Paleozoic age, the North Atlantic rifting, the Late Cretaceous alkaline magmatism (intrusive and extrusive), the Alpine tectonic inversion and the Quaternary reactivation of the passive margin. We present results from the compilation of a series of marine magnetic surveys conducted along the Portuguese nearshore from 2014 to 2019. Magnetic data were acquired with 1 nautic mile line separation, resulting in near full coverage of the nearshore along a 120 km long margin segment, from Sintra to Odeceixe. For a large part of the surveyed area, ultra-high resolution seismics and multibeam bathymetry were simultaneously acquired. Magnetic data were processed to produce high resolution mapping of magnetic anomalies, and also to enhance both shallow and deep structures, using several derivative and filtering techniques. We combine the interpretation of high-resolution magnetic mapping with the interpretation of ultra-high resolution and vintage deep penetration seismic data to infer the local and regional expression of tectonic structures and magmatic bodies. Our results allow: identifying the offshore extension of important faults, e.g. the Grândola, Pinhal Novo and Messejana faults; resolving previously blurry-imaged magmatic structures, e.g. Sines and Cabo Raso anomalies; identifying faults recycled from the Paleozoic through Present; constraining the relation between magmatic intrusions and faults; and bringing constraints to the discussion of magmatic emplacement.

The Prairie Pothole Region of North America is characterized by millions of depressional wetlands, which provide critical habitats for globally significant populations of migratory waterfowl and other wildlife species. Due to their relatively small size and shallow depth, these wetlands are highly sensitive to climate variability and anthropogenic changes, exhibiting inter- and intra-annual inundation dynamics. Moderate-resolution satellite imagery (e.g., Landsat, Sentinel) alone cannot be used to effectively delineate these small depressional wetlands. By integrating multi-temporal (2009-2018) NAIP aerial imagery and ancillary geospatial datasets, a fully automated approach was developed to delineate wetland inundation extent at watershed scales using Google Earth Engine. Machine learning algorithms were used to classify aerial imagery with additional spectral indices to extract potential wetland inundation areas, which were further refined using ancillary geospatial datasets. The wetland delineation results were then compared to the U.S. Fish and Wildlife Service National Wetlands Inventory (NWI) geospatial dataset and existing global-scale surface water products to evaluate the performance of the proposed method. The results showed that the proposed method can not only delineate the most up-to-date wetland inundation status, but also demonstrate wetland hydrological dynamics, such as wetland coalescence through fill-spill hydrological processes. The proposed automated algorithm provides a practical, reproducible, and scalable framework, which can be easily adapted to delineate wetland inundation dynamics at broad geographic scales.

We studied seven earthquakes in the southern East African Rift System (EARS) with catalog depths of 10 to 33km, in locations where the Moho is thought to be at ~32 km depth (CRUST 1.0). Our earthquakes include three relocated by Yang and Chen (JGR, 2010) to be significantly deeper and to be below the Moho. We independently assessed whether the events occurred above or below the Moho using the Sn/Lg method (Wang et al., AGU Fall Meeting 2019; see also adjacent poster by Chen et al.). In a 1D earth, sub-Moho earthquakes produce strong Sn and weak Lg signals, and intra-crustal earthquakes produce weak Sn and strong Lg arrivals. All seven events we studied were characterized by low Sn/Lg, including the three earthquakes interpreted as upper-mantle events by Yang and Chen (2010) (their events M3 and M5 in Malawi and T12 in Zambia). Although low Sn/Lg is elsewhere associated with crustal events we suspect that, in the East African Rift, events in the shallow upper mantle that produce strong Sn at the source may be recorded at regional distances with low Sn/Lg due to Sn-to-Lg conversion at the deepening Moho at the rift margins. CRUST 1.0 suggests crustal thicknesses reach 45 km beneath the cratons adjacent to the East African Rift, with average Moho dips of 5-10°. Hence even the deepest earthquake reported by Yang and Chen (JGR, 2010), at 44±4 km, could undergo significant Sn-to-Lg conversion. Our findings highlight the importance of careful interpretation of Sn/Lg ratios and motivates our ongoing work to model 2D propagation effects.