Exposure Dating Research Articles

The Tutupaca volcanic complex (Southern Peru): Eruptive chronology and successive destabilization of a dacitic dome complex

Several processes have been proposed as triggering mechanisms for the large sector collapses that affect most volcanoes, and which may occur several times in the volcano's lifetime. Here we present and discuss the case of Tutupaca volcano, located in southern Peru and part of the Central Volcanic Zone of the Andes. Tutupaca is composed of an old, hydrothermally altered and highly eroded Basal edifice, as well as younger twin peaks located in the northern part of the complex (the Western and Eastern Tutupaca). The youngest Eastern edifice of Tutupaca is composed of at least seven coalescing lava domes and associated deposits, including block-and-ash flow and debris avalanche deposits. We identified two debris avalanche deposits. An older unit (Azufre debris avalanche deposit) was channeled in the valleys located to the E and SE of the basal volcano, reaching up to 3.5 km from its source region. Four cosmogenic nuclide exposure dates (10Be/feldspar) were obtained from boulders of this debris avalanche deposit and ranged between 6.0 ± 0.7 and 7.8 ± 1.5 ka. The younger unit (Paipatja deposit) was associated with the sector collapse of the edifice reconstructed just after the first debris avalanche (domes IV to VIII). The sector collapse produced a debris avalanche deposit that outcrops immediately to the NE of the amphitheater and was associated with a large pyroclastic density current deposit that was previously dated by radiocarbon at 218 ± 14 a BP (Samaniego et al., 2015). Both debris avalanche deposits have two contrasting sub-units: (1) the main subunit, hereafter called hydrothermal-altered debris avalanche deposit, is a whitish-yellow volcanic breccia with heterolithic and heterometric blocks, which originated from the Basal edifice, and (2) a dome-rich debris avalanche deposit, composed by non-altered dome blocks from Eastern Tutupaca. In proximal areas, the dome-rich unit overlaps the hydrothermally-altered unit while in distal areas, these two units are mixed forming a hummocky and/or ridged topography. In addition to the similarity of both debris avalanches, we propose that the triggering mechanism for these debris avalanches was similar. The dacitic dome growth, coupled with a substrate of older, hydrothermally-altered rock, induced the destabilization of the edifice, producing the debris avalanches and the related pyroclastic density currents.

Interplay of fluvial incision and rockfalls in shaping periglacial mountain gorges

Fluvial incision is the consequence of landscape readjustment to combined tectonic and climatic processes. In the southwestern Alps (Haute Provence Geopark), deep gorges incised by the Bès River attest of efficient erosional processes at the front of the Alpine mountain range. This catchment stands in a peripheral Alpine position, out of the glaciated domain during the last glacial periods, which makes it suitable to quantify fluvial incision and related erosional processes in a glacier-free environment. In this paper, we combine high resolution 3D topographic mapping and in situ produced cosmogenic 36Cl dating of a mountain gorge (the “Clue de Barles” Gorge). First, the very high-resolution 3D topographic modeling from aerial and drone surveys permits to map the erosion markers on the gorge walls and to accurately determine the topographic shielding factor for Cosmic Ray Exposure (CRE) dating. Secondly, 36Cl CRE age distribution highlights two distinct geomorphic domains along the vertical profile: i) the higher section is characterized by clusters of similar CRE ages, interpreted as related to paraglacial rockfall events; ii) the lower section shows increasing ages with height, which are ascribed to fluvial incision occurring at a rate of 0.15 mm/yr since 25 ka, and of 2 mm/yr since 2 ka. Our results for the Clue de Barles, compared to other sites in the South French Alps highlight that: i) the gorge morphology is the result of the combination of both vertical fluvial incision and lateral gravitational processes, ii) the mean Quaternary fluvial incision rate in the Bès River catchment is at least twice lower than further east in the formerly glaciated Alps.

Empirical evidence for cosmogenic 3He production by muons

Cosmic ray muons penetrate deeply into rock where they interact with atoms to produce cosmogenic nuclides. Incorporation of the muon contribution to the production rates of cosmogenic nuclides increases the accuracy of exposure dates, burial ages, and erosion rates inferred from measured nuclide concentrations. In the absence of empirical evidence, it is generally assumed that muons do not produce 3He, a cosmogenic nuclide commonly used for exposure dating. Here we assess whether muons produce 3He by measuring He isotope concentrations in pyroxene and ilmenite from a ∼300 m deep drill core and other subsurface samples of the mid-Miocene Columbia River Basalt in Washington, USA. 3He concentrations in our samples exhibit an exponential decline with depth with an e-folding length of 32.4 m, which corresponds to an attenuation length for 3He production of 8780 g cm−2. The deeply penetrating exponential is diagnostic of 3He production by cosmic ray muons. Assuming no erosion, we constrain the minimum surface muonogenic production rate to be 0.23 atom g−1 pyroxene yr−1, whereas when incorporating erosion the production rate is 0.45 atom g−1 pyroxene yr−1. 3He concentrations in samples deeper than ∼100 meters are consistent with model-based estimates of depth-independent nucleogenic production from the capture by 6Li of neutrons produced by alpha particle reactions on light elements. Measurements in other subsurface samples indicate that muon-produced 3He is prevalent across the Columbia Plateau. The penetration depth of muonogenic 3He production is substantially deeper, and the ratio of muon- to spallation-produced 3He is substantially lower, than found for other cosmogenic nuclides. Our results provide the first definitive empirical evidence for 3He production by muons, which has several implications for quantifying the timing and rates of Earth surface change and interpreting He isotope ratios. Importantly, despite the low production rates, landforms in the Channeled Scablands, which were formed by incision of the Columbia River Basalt by the late-Pleistocene Missoula floods, have high concentrations of 3He inherited from post-Miocene muon exposure. Hence 3He production by muons must be considered, particularly when dating rapid erosional events in old bedrock. Our findings indicate samples with less than several tens of meters of shielding by overlying rock will contain cosmogenic 3He that elevates 3He/4He ratios. Hence caution should be used when using 3He/4He ratios from samples at shallower depths to infer mantle sources of basalt.

36Cl exposure dating of the Mahu Giant landslide (Sichuan Province, China)

Abstract Age is of great significance to understanding the causes of landslide instability and movement, and therefore, it is important to know when conducting a hazard assessment. To date, no detailed and comprehensive determination of the age of the Mahu giant landslide has been conducted. The Mahu giant landslide is located in the lower reaches of the Jinsha River and has a volume of 2.38 km3 and a maximum elevation difference of 1080 m, making it the largest subaerial landslide found to date in China. In this study, we report the age of the landslide based on 36Cl exposure dating. Ten cosmogenic nuclide samples were collected from boulders on the landslide deposits and the bedrock on the landslide's scarp, and eight valid ages were derived in the range of 11.63 ± 0.96 to 29.14 ± 1.81 ka. Based on the lithologies and ages of the landslide's scarp and the deposits, the landslide is concluded to have been formed by two major events, with error weighted mean ages of 14.75 and 25.21 ka. The age results for the Mahu landslide obtained in this study provide a basis for understanding the causes of the Mahu landslide. Moreover, this case study indicates that the regional fault activity and earthquake risk can be analyzed from the perspective of landslide science.

Paleoglacial and paleoclimate reconstructions during the global Last Glacial Maximum in the Longriba area, eastern Tibetan Plateau

Owing to the remoteness of the Longriba area and the lack of dating records, it is extremely challenging to reconstruct the chronology and extent of the paleoglaciers in this area. In this paper, we combined limited observational data with automated modelling for paleoglacial reconstructions. We first identified a broadly distributed paleoglacier from satellite imagery and field investigation based on the sediment-landform assemblage principle and dated it to 23.1±1.4∼19.5±1.2 ka by 10Be exposure dating, corresponding to the global Last Glacial Maximum (gLGM). Then, we reconstructed the extent and ice surface of 171 paleoglaciers formed during the similar period based on geomorphological evidence and ‘ice surface profile’ modelling. The results showed that the paleoglacial coverage was 426.5 km2, with an ice volume of 38.1 km3, in the Longriba area. The reconstructed equilibrium line altitudes (ELAs) based on modelled ice surfaces yielded an average of 4245±66 m above sea level (asl), ∼725±73 m lower than the present ELA (4970±29 m asl). The temperature was ∼5.51–6.68 °C lower, and the precipitation was ∼30–34% less in Longriba, during the gLGM compared to the present day. This glacial advance was mainly driven by colder climate that was synchronous with Northern Hemisphere cooling events.

Assessment of Day-7 Postexposure Testing of Asymptomatic Contacts of COVID-19 Patients to Evaluate Early Release from Quarantine — Vermont, May–November 2020

On May 8, 2020, the Vermont Department of Health (VDH) issued a Health Update* recommending shortening the duration of quarantine for persons exposed to SARS-CoV-2, the virus that causes coronavirus disease 2019 (COVID-19). Exposed persons who were in quarantine could be tested by polymerase chain reaction (PCR) on or after quarantine day 7. Those who had remained asymptomatic throughout quarantine and who received a negative SARS-CoV-2 PCR test result on or after day 7 could end quarantine. This policy was based on a report suggesting that symptom onset occurs within this time frame in approximately three quarters of COVID-19 cases (1) and on consultation of the Vermont Health Commissioner with the U.S. Surgeon General. VDH implemented this policy to minimize restrictions on state residents, recognizing that some reduction could occur in the prevention benefit of quarantine to contain the spread of SARS-CoV-2. State-run SARS-CoV-2 testing sites were made available to increase access to no-cost testing and facilitate implementation of this policy. During August 1-December 1, among persons seeking testing at a VDH SARS-CoV-2 testing site, 36% stated that their reason for seeking testing was to end quarantine early (VDH, unpublished data, December 7, 2020), indicating that persons were aware of and following the policy and using the testing services provided. To assess the effectiveness of this policy, VDH analyzed testing data for contacts of persons with a COVID-19 diagnosis. During May 8-November 16, VDH identified 8,798 exposed contacts of COVID-19 patients; 3,983 (45%) had sought testing within 14 days of their exposure, with day 0 defined as the date of last exposure noted in the case investigation record. Among these persons, 2,200 (55%) who received testing on days 7-10 were included in this analysis; 977 (44.9%) of these contacts had a specimen collected for testing on day 7. Among these, 34 (3%) had test results that were positive, 940 (96%) had results that were negative, and three (<1%) had results that were indeterminate (Table). Among the 34 contacts who received a positive SARS-CoV-2 PCR test result on day 7 after exposure, 12 (35%) were asymptomatic. The remaining 22 contacts with positive test results were symptomatic at the time of testing; approximately one half had developed symptoms on days 4-7 after exposure. Among the 940 contacts who received negative test results on specimens collected on day 7 after exposure, 154 (16%) had a subsequent test within the next 7 days (i.e., days 8-14); among these, 152 (99%) had tests that remained negative, and two (1%) had results that were indeterminate.

Contact tracing in COVID-19: Justifying the need and strengthening the process

The Corona Virus Disease 2019 (COVID-19) pandemic continues to rise in terms of its geographical distribution, the number of people infected and the number of people losing their lives due to the resulting complications. Contact tracing is an effective strategy to identify, assess and manage people with a positive history of exposure to a confirmed case, so that we succeed in interrupting the transmission chain and further transmission of infection. It is essential to follow-up the contacts for a period of 2 weeks from the last date of exposure, but the successful implementation of this strategy will depend upon the support of the general population, planning of the entire process after considering the local contexts, trained and adequate number of workforce, logistics, and a supportive mechanism to collect, compile and analyze the data in real-time. In conclusion, the component of contact tracing is a crucial link in interrupting the chain of transmission of the COVID-19. It is the responsibility of the public health authorities and members of the community to work in close collaboration to identify the contacts at the earliest and quarantine them with an aim to prevent onward transmission.

Risk Factors, Epidemiological and Clinical Outcome of Close Contacts of COVID-19 Cases in a Tertiary Hospital in Southern India

Introduction: The knowledge of epidemiologic characteristics and transmission dynamics of a novel pathogen, such as Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2) among close contacts can help in planning and development of effective control policies in different parts of the world. Aim: To assess the epidemiological and clinical outcome of close contacts of Coronavirus Disease (COVID-2019) cases admitted in a tertiary COVID hospital and to assess the role of risk factors in predicting the epidemiological outcome of these contacts. Materials and Methods: The current retrospective cohort study was conducted among 1286 close contacts of COVID-19 patients admitted to Government Medical College, Thrissur, Kerala. The data collection was done by a semi-structured telephonic interview by the contact tracing team. The questions included the type of exposure to the index case, symptoms if any, date of last exposure with COVID-19 positive patients, and final COVID-19 status of the contact at the end of 14 days. The association of risk factors of COVID-19 positivity was done using binary logistic regression. Results: Proportion of close contacts of COVID-19 who developed the disease was 24.2% (21.87-26.52%). The mean incubation period was found to be 4.22 days (C.I-3.71-4.65). The serial interval mean was found to be 5.24 days (C.I 4.764-5.716). The proportion of household contacts of COVID-19 cases who developed the disease was found to be 26% (C.I-23%-29%). The majority (52.4%) of infections among contacts were asymptomatic. Most common symptom among the COVID-19 positive was fever (32.8%) followed by cough (16.1%). The most common risk factors of infection among primary close contacts were sharing the same room (adjusted odds ratio-2.394) and common use of fomites (adjusted odds ratio-1.953) while use of a mask was found to be protective (adjusted odds ratio-0.570). Significant factors associated with the type of contact with infection were workplace-related contact (adjusted odds ratio-6.629), household contact (adjusted odds ratio-4.856), and travel-related contact (adjusted odds ratio-2.899). Conclusion:The study concludes important risk factors of transmission among close contacts of COVID-19 as being in a household, workplace and travel related contact where the use of mask was found to be protective. The study also concludes that most of the COVID-19 infections in close contacts are asymptomatic.

Selective serotonin reuptake inhibitors use and hepatocellular carcinoma in patients with alcohol use disorder

BackgroundResearch has proposed that selective serotonin reuptake inhibitors (SSRIs) were associated with a reduction of the risk of hepatocellular carcinoma (HCC). The objective of this study is to investigate whether SSRIs use is associated with decreased risk of HCC in patients with alcohol use disorder (AUD). Patients and methodsWe conducted a retrospective population-based cohort study using Taiwan’s National Health Insurance Research Database (NHIRD) from 1997 to 2013 and enrolled patients with newly diagnosed AUD. After propensity scores matching at a ratio 1:4, total of 4945 SSRI users and 19,785 non-SSRI users were included in the matched cohort. Patients were followed up from the 365th day after the date of first exposure to SSRIs to occurrence of HCC, the date of death, or the end of 2013. Cox proportional hazard regressions were performed to evaluate hazard ratio (HRs) for HCC in SSRI-exposed patients compared with unexposed patients. ResultsIn the main study cohort, SSRI use was associated with significant lower risk of HCC compared to the non-SSRI users after adjusting for age, sex, income, urbanization, alcoholic fatty liver, alcoholic hepatitis and diabetes (adjusted hazard ratio [aHR] = 0.31, 95 % CI = 0.24−0.39). The negative association of SSRI use and HCC was replicated in the matched cohort (aHR = 0.58, 95 % CI = 0.44−0.77). The effect of SSRI use on HCC was dose-related in both cohorts (p for trend < 0.0001). ConclusionsThis study showed that SSRIs use was associated with a reduction risk of HCC among AUD patients in a cumulative dose effect manner.

Schmidt hammer exposure dating for brick masonry

This research investigates the validity of the Schmidt hammer exposure dating (SHED) technique as a complementary means to date monuments according to the evaluation of the brick decay from masonry exposed to climatic conditions. The degree of surface weathering, I&lt;sub&gt;5&lt;/sub&gt; (%) is calculated as an indicator of the ageing effect and compared to the absolute age of the churches constructed between 1600 and 1795. This paper discusses the results obtained with such a method and the use of the technique within the framework of historical research. Tests were done on exterior church walls built between the 17&lt;sup&gt;th&lt;/sup&gt; and 19&lt;sup&gt;th&lt;/sup&gt; centuries. All the churches were located within the limited geographical area of Hainaut, in the south of Belgium. Results indicate that SHED provides encouraging results for buildings constructed between 1790 and 1895, with a linear correlation (R&lt;sup&gt;2&lt;/sup&gt;&gt;0.8) between surface weathering of brick façades and their ages. However, the weathering indices show high variability of values for the period 1750−1790, which may confirm that the variable qualities of bricks were in use during this period of time because of the different production techniques. As such, the results highlight the probable influence of the entire manufacturing and construction process and technical improvements in traditional brick-making.

10Be surface exposure dating of the deglaciation of northernmost Norway and Finland

During the Last Glacial Maximum, the coast of Finnmark county, northern Norway, was covered by the Scandinavian Ice Sheet (SIS), which coalesced with the Barents Sea Ice Sheet (BSIS) off the coast. The region is thus important for our understanding of the dynamic interactions between the BSIS and the SIS, yet it remains one of the least dated regions covered by the SIS. To improve the chronological constraints, we present 23 new 10Be ages from eight localities in northernmost Norway and Finland, and discuss implications for the pattern and timing of ice‐sheet retreat in the region. The samples were collected along a 240‐km‐long north–south transect ranging from the outer coast of Nordkinn peninsula (Norway) to Lake Inarijärvi (Finland). The new exposure ages indicate deglaciation of the outer coast at ~14.5 ka. From there, the ice retreated southward until it reached the Main substage moraine complex just north of the Norwegian‐Finnish border during the Younger Dryas. South of the Main substage moraines the deglaciation appears to have become more rapid, eventually reaching Inari, at the southern end of our transect, around 10.4±1.4 ka.

Regression Discontinuity Designs in Health: A Systematic Review.

Regression discontinuity designs are non-randomized study designs that permit strong causal inference with relatively weak assumptions. Interest in these designs is growing but there is limited knowledge of the extent of their application in health. We aimed to conduct a comprehensive systematic review of the use of regression discontinuity designs in health research. We included studies that used regression discontinuity designs to investigate the physical or mental health outcomes of any interventions or exposures in any populations. We searched 32 health, social science, and gray literature databases (1 January 1960 to 1 January 2019). We critically appraised studies using eight criteria adapted from the What Works Clearinghouse Standards for regression discontinuity designs. We conducted a narrative synthesis, analyzing the forcing variables and threshold rules used in each study. The literature search retrieved 7658 records, producing 325 studies that met the inclusion criteria. A broad range of health topics was represented. The forcing variables used to implement the design were age, socioeconomic measures, date or time of exposure or implementation, environmental measures such as air quality, geographic location, and clinical measures that act as a threshold for treatment. Twelve percent of the studies fully met the eight quality appraisal criteria. Fifteen percent of studies reported a prespecified primary outcome or study protocol. This systematic review demonstrates that regression discontinuity designs have been widely applied in health research and could be used more widely still. Shortcomings in study quality and reporting suggest that the potential benefits of this method have not yet been fully realized.

A novel method to evaluate chemical concentrations in muddy and sandy coastal regions before and after oil exposures.

Oil spills can result in changes in chemical concentrations along coastlines. In prior work, these concentration changes were used to evaluate the date sediment was impacted by oil (i.e., oil exposure date). The objective of the current study was to build upon prior work by using the oil exposure date to compute oil spill chemical (OSC) concentrations in shoreline sediments before and after exposure. The new method was applied to OSC concentration measures collected during the Deepwater Horizon oil spill with an emphasis on evaluating before and after concentrations in muddy versus sandy regions. The procedure defined a grid that overlaid coastal areas with chemical concentration measurement locations. These grids were then aggregated into clusters to allow the assignment of chemical concentration measurements to a uniform coastal type. Performance of the method was illustrated for ten chemicals individually by cluster, and collectively for all chemicals and all clusters. Results show statistically significant differences between chemical concentrations before and after the calculated oil exposure dates (p<0.04 for each of the 10 chemicals within the identified clusters). When aggregating all chemical measures collectively across all clusters, chemical concentrations were lower before oil exposure in comparison to after (p<0.0001). Sandy coastlines exhibited lower chemical concentrations relative to muddy coastlines (p<0.0001). Overall, the method developed is a useful first step for establishing baseline chemical concentrations and for assessing the impacts of disasters on sediment quality within different coastline types. Results may be also useful for assessing added ecological and human health risks associated with oil spills.

Clastogenic effect by recreative exposure to marijuana in individuals from the Estado de Mexico: Pilot study

Cannabis sativa is the most trafficked illicit substance in the world, 147 million people consume it recreationally. This plant contains more than 100 phytocannabinoids, the most important being 1-delta-9- tetrahydrocannabinol (THC). The genotoxic effect of cannabinoids has been proven in vitro and in vivo models, where damage to nuclear DNA and chromosomal aberrations (CA) was observed. This shows the clastogenic potential of this drug. In this research, we study genotoxic damage in Mexican individuals recreationally exposed to marijuana. The study of chromosomal aberrations was performed in 48 hour lymphocyte cultures of 30 exposed and 30 no exposed individuals. 100 metaphases were analyzed per sample. The type of CA was identified and counted. The number of CAs identified in the exposed group was 344 with a median of 9.5; the no exposed group had 218 CAs, with a median of 6.5. The statistical analysis showed a significant difference between both groups, p=0.013. Chromatid and chromosomal breaks were the most frequent aberrations. Comparing the exposure time vs. frequency of CA in the exposed group, we did not find a significant difference between sub-groups from 1 to 5 and 6 to 11 years. Similarly, in the analysis of the last exposure date vs CA, no significant differences were observed between the subgroups &lt;1 week and &gt;1 week. Our results show an increase in the frequency of the number of CAs in the individuals recreationally exposed. These results show evidence of the genotoxic potential of marijuana.

Geomorphic response to the Lateglacial–Holocene transition in high Alpine regions (Sanetsch Pass, Swiss Alps)

Several palaeoclimatic archives have documented the pronounced climatic and environmental change associated with the Lateglacial–Holocene transition in the European Alps. However, the geomorphic response to this major environmental transition has only been punctually investigated. In this study, we propose a detailed reconstruction of post‐Last Glacial Maximum palaeoenvironmental conditions and geomorphic connectivity in the Sanetsch Pass area (2252 m a.s.l., western Swiss Alps) based on a multi‐method approach combining geomorphological and sedimentological field investigations with quantitative sedimentology and geochronology. Samples for sediment characterization (grain size, micromorphology and X‐ray diffraction) and geochronology (optically stimulated luminescence and 10Be surface exposure dating) were collected from three representative landforms of the study area: a high‐elevation silty deposit covered by patterned ground, an alluvial fan, and a hummocky moraine covered by rockfall deposits. Our results reveal the geomorphic history of the three deposits and their connectivity through sediment cascade. These results highlight the development of rapid and most probably transient landscape changes in high Alpine regions during the Lateglacial–Holocene transition, with an increase in sediment flux and the establishment of paraglacial and periglacial geomorphic processes.

The last glaciation of the Arctic volcanic island Jan Mayen

The volcanic island of Jan Mayen, remotely located in the Norwegian‐Greenland Sea, was covered by a contiguous ice cap during the Late Weichselian. Until now, it has been disputed whether parts of the island south of the presently glaciated Mount Beerenberg area were ever glaciated. Based on extensive field mapping we demonstrate that an ice cap covered all land areas and likely also extended onto the shallow shelf areas southeast and east of the island. Chronological interpretations are based on K‐Ar and 40Ar/39Ar dating of volcanic rocks, cosmogenic nuclide (36Cl) surface exposure dating of bedrock and glacial erratics, and radiocarbon dating. We argue that ice growth started after 34 ka and that an initial deglaciation started some 21.5–19.5 ka in the southern and middle parts of the island. In the northern parts, closer to the present glaciers, the deglaciation might have started later, as evidenced by the establishment of vegetation 17–16 cal. ka BP. During full glaciation, the ice cap was likely thickest over the southern part of the island. This may explain a seemingly delayed deglaciation compared with the northern parts despite earlier initial deglaciation. In a broader context, the new knowledge of the Late Weichselian of the island contributes to the understanding of glaciations surrounding the North Atlantic and its climate history.

Zastosowanie ziemskich izotopów kosmogenicznych w datowaniu glin lodowcowych – potencjał, ograniczenia i perspektywy badawcze

Application of in situ cosmogenic nuclides in dating glacial till – research potential, limitations and prospects. A b s t r a c t. Determination of numerical age for glacial till is one of the most intriguing issues in glacial geology and geomorphology. Till layers are unequivocal evidence of ice sheets advances and retreats, and therefore they are very important for Quaternary palaeoclimatic reconstructions. Herein, we present a review dedicated to the methodology of glacial till dating with in situ cosmogenic nuclides. This relatively novel approach enables direct dating of deposition of till and its exposure after deglaciation. Getting reliable numerical age (in years) of till opens a new prospect for reconstructions of past glaciations and palaeogeographic studies. Despite some limitations of applying in situ cosmogenic exposure and burial dating, we argue that this technique may be successfully employed in studies of glacial deposits in Poland.

Progress on the incubation period of COVID-19

<p indent="0mm">Coronavirus disease 2019 (COVID-19) is an emerging infectious disease caused by SARS-CoV-2. Effective treatments are still lacking. The incubation period of COVID-19 is the period between the infection of an individual by a pathogen (SARS-CoV-2) and the manifestation of the illness or disease. The incubation period is one of the important epidemiological parameters of infectious diseases. The study of the incubation period of COVID-19 is of great significance for better understanding the natural history of the disease, tracing the source of infection, determining the detention, quarantine and isolation of contacts, determining the time of immunization, and making prevention and control measures. This study mainly reviews the progress of the incubation period of COVID-19. In previous studies, a direct calculation or parameter estimation method is usually used to estimate the incubation period, and the commonly used distributions are lognormal distribution, Weibull distribution, Gamma distribution, etc. Due to the differences in the study population, data sources and estimation methods, there are differences in the estimation results of the incubation period of COVID-19 in various studies. The estimated median incubation period for COVID-19 was about <sc>5.9 d</sc> (95%CI: 2.98−10.51) and the average incubation period was about <sc>5.7 d</sc> (95%CI: 4.3−8.9). The median incubation period for COVID-19 was estimated to be about <sc>5.2 d</sc> (95%CI: 3.0−11.9) in studies using the direct calculation method, and about <sc>5.25 d</sc> (95%CI: 3.57−8.19) in studies using the parameter estimation method. To calculate the incubation period of COVID-19, it is important to accurately collect the date of exposure and the date of symptoms onset. Due to the diversity of COVID-19 transmission routes and the possibility of multiple exposures to the same source of infection or to different sources of infection, it is often difficult to determine the exact exposure time for some patients, which brings the difficulty to the accurate estimation of the incubation period. The choice of methods depends on the epidemiological data of the study population and application scenarios. For example, in the early stage of an outbreak, when the incubation period data of small samples of infected persons are quickly obtained through field epidemiological investigation, it is advisable to adopt the direct calculation method for rapid estimation and timely guidance for prevention and control measures. As the epidemic progresses, when more epidemiological survey data are available, the parameter estimation method is a better choice. The optimal method can be selected for estimation. Either direct calculation or parameter estimation method, the accuracy of the data is crucial. Therefore, the recall bias should be minimized to obtain relatively accurate data at each key time point. At the same time, a more accurate estimate of the incubation period can be obtained by taking the infector-infected pairs with a clear transmission chain as the study population.

Earthquake Hazard Uncertainties Improved Using Precariously Balanced Rocks

AbstractProbabilistic seismic hazard analysis (PSHA) is the state‐of‐the‐art method to estimate ground motions exceeded by large, infrequent, and potentially damaging earthquakes; however, a fundamental problem is the lack of an accepted method for both quantitatively validating and refining the hazard estimates using empirical geological data. In this study, to reduce uncertainties in such hazard estimates, we present a new method that uses empirical data from precariously balanced rocks (PBRs) in coastal Central California. We calculate the probability of toppling of each PBR at defined ground‐motion levels and determine the age at which the PBRs obtained their current fragile geometries using a novel implementation of cosmogenic 10Be exposure dating. By eliminating the PSHA estimates inconsistent with at least a 5% probability of PBR survival, the mean ground‐motion estimate corresponding to the hazard level of 10−4 yr−1 (10,000 yr mean return period) is significantly reduced by 27%, and the range of estimated 5th–95th fractile ground motions is reduced by 49%. Such significant reductions in uncertainties make it possible to more reliably assess the safety and security of critical infrastructure in earthquake‐prone regions worldwide.

Late Quaternary Tectonic Activity and Slip Rates of Active Faults in the Western Hexi Corridor, NW China

The Yinwashan and Xinminpu faults are located in the Jiuxi Basin in the western end of the Hexi Corridor. The determination of their activity and slip rates is of great significance for understanding the eastward extension of the Altyn Tagh fault. Based on geological and geomorphologic field survey, trench excavation, optically stimulated luminescence dating, we define the fault geometry and kinematic properties of the two faults. Based on fault scarps measurement using differential GPS and 10Be surface exposure dating, we determined vertical slip rate of 0.09±0.01 mm/yr for the Yinwashan fault and 0.1±0.02 mm/yr for the Xinminpu fault. Using the dips observed in trenches and natural sections, we estimated horizontal shortening rates of 0.05±0.03 and 0.23±0.06 mm/yr, respectively. No significant strike slip motion is observed on these two faults, and we infer that this region was dominated by horizontal shortening in the Late Quaternary. Although the shortening rate is quite low on each individual fault, together with other faults in this area, these two faults have an essential role in transferring slip from the eastern end of the Altyn Tagh fault and in accommodating the northeastward growth of Tibetan Plateau.