Weak Events Research Articles

Reconciliation of Theoretical Lifetimes of the 5s5p Metastable State for 88Sr with Measurement: The Role of the Blackbody-Radiation-Induced Decay

We conducted measurement and calculation to resolve the long-standing large discrepancy in the metastable state lifetime for the 88Sr atom between theoretical and experimental results. The present lifetime s, measured using the magneto-optical trap as a photon amplifier to detect the weak decay events, is approximately 60% larger than the previous experimental value s. By considering the electron correlation effects in the framework of the multiconfiguration Dirac–Hartree–Fock theory, we obtained a theoretical lifetime of 1079(54) s, which lies in the range of measurements with error bars. Furthermore, we considered the higher-order electron correlation and Breit interaction to control the uncertainty of the theoretical calculation. The significant improvement in the agreement between calculations and measurements is attributed to the updated blackbody radiation-induced decay rate.

Boulder Detection in the Shallow Sub‐Seafloor by Diffraction Imaging With Beamforming on Ultra‐High Resolution Seismic Data—A Feasibility Study

AbstractSmall‐scale heterogeneities within the seafloor such as glacial boulders, concretions, or unexploded ordnance are of major scientific and economic interest. Because of their small size, such objects are hardly imageable by conventional seismic methods since they produce only faint diffractions. Despite the growing interest, reliable and efficient object detection methods are still not established. So, a marine acquisition system to image objects in the size range 0.3–4.1 m in the near‐surface has been designed and workflows have been developed. Source signals with a central frequency of ∼1,000 Hz are necessary to generate diffractions for the object size range. Performing beam pattern analyses, a rigid tow frame with the dimensions 8 × 3 m and attached hydrophones was designed. A synthetic aperture approach is realized to improve the resolution. Reflection events are suppressed in Normal‐Move‐Out corrected shot gathers by the muting of high singular values to enhance the diffractions. The diffractions are imaged with a beamforming algorithm with a high efficiency, as a total swath angle of about 80° in across‐track direction is covered. The processing of synthetic data sets allows an optimization and validation of the workflow and sensitivity analyses. Ground truthing is achieved with 1–2 m large boulders on the seafloor in 22 m depth, which were identified in a Multi‐Beam Echo Sounder data set. Although diffractions are only weak events in seismic data sets, 3D object detection with seismic beamforming has been found to be an efficient and reliable method to perform derisking for offshore infrastructure installations, drillings, or geologic interpretation.

Assessment of the Mining Technology Influence to the Level of Seismic Activity by Geomechanical Modeling and Field Observations Data

Based on a retrospective analysis, an original approach was verified that allows establishing quantitative relationships between the parameters of deterministic and stochastic processes of various physical nature. The approach consists in revealation of statistically significant correlations between long time series of key parameters of these processes, recorded in different spatial regions of target object. Within the framework of this approach, a space-time analysis of technogenic seismicity (hypocenter coordinates, time and energy of weak and moderate dynamic events) at the Tashtagol iron ore deposit was performed in conjunction with geomechanical modeling of the stress field evolution due to mining. Using the obtained correlation dependences between the number of dynamic events and the integral characteristic of the stress state, a forecast was made for the number of dynamic events in different areas of the geomechanical space of the deposit under various mining technologies. Comparison of the results shows that due to backfill array construction, as a rule, the level of seismic activity decreases.

Spatiotemporal propagating decadal signal of ocean heat content and thermocline depth identified in the tropical Pacific

Tropical Pacific decadal variability (TPDV) and its mechanisms are essential for understanding long-term variations in global climate. The spatiotemporal pattern of this decadal variation has yet to be clarified. Here, on the basis of observational data with the help of the adaptive data analysis method, we extracted and investigated the spatiotemporal evolution of the tropical Pacific decadal variability in upper ocean heat content (UOHC) and thermocline depth. The tropical decadal signal propagated eastward along the equator from the western Pacific to the eastern Pacific after the 1970s, with a speed of 4–5 cm s−1 yielding a decadal oscillation of approximately 11–13 years. This decadal variability of the thermocline fluctuations (UOHC) was proven to be closely correlated with western wind anomalies since the 1970s and may have been induced by the regime shift of the Pacific decadal oscillation. These peaks of decadal signals corresponded well with the strong El Niño–Southern Oscillation (ENSO) events, reflecting nonlinear rectification of ENSOs on TPDV. Moreover, the TPDV showed a modulating signal on moderate and weak ENSO events.

Impact of Strong and Weak Stratospheric Polar Vortices on the Mesosphere and Lower Thermosphere

AbstractThe impact of strong and weak Northern Hemisphere stratospheric polar vortices on the zonal mean and atmospheric tides in the mesosphere and lower thermosphere (MLT) is investigated using Specified Dynamics Whole Atmosphere Community Climate Model (WACCM) with thermosphere‐ionosphere eXtension (SD‐WACCM‐X) simulations and Aura Microwave Limb Sounder observations. The observed and simulated zonal mean anomalies during strong and weak vortices are in good agreement. Zonal mean and tidal anomalies during weak polar vortex events are consistent with those known to occur during sudden stratospheric warmings. Generally opposite, though weaker, anomalies are found to occur when the stratospheric polar vortex is strong. The most notable impact in the MLT is a reduction in the migrating semidiurnal tide of ∼25%–35% during strong polar vortex times. The results demonstrate that, in addition to weak polar vortex events, a strong stratospheric polar vortex can also have an appreciable impact on the middle and upper atmosphere.

Data-driven reflection imaging based on seismic interferometry

In conventional land seismic exploration, shallow seismic reflections with low fold are usually contaminated by noise and most conventional acquisition geometries struggle to produce sufficient near-offset fold to process shallow seismic reflections based on the velocity model. Deep seismic reflections tend to occur as weak events due to seismic wave absorption and attenuation. To enhance the shallow and deep seismic reflections, we have developed a data-driven reflection imaging method based on seismic interferometry of cross-coherence type, which first retrieves coherent reflections by cross-coherence of full wavefields with zero-offset reflections and then achieves imaging results with high quality by summing all of the crosscorrelations of full wavefields with coherent reflections in a common-midpoint gather. The novel purely data-driven method does not require any velocity information and can flatten noisy interfering reflection events with no waveform distortions. The focusing effects, which represent the stack of all the seismic reflection events, increase the fold of weak seismic reflections and further significantly improve the signal-to-noise ratio of imaging results. In comparison with data-driven reflection imaging methods based on seismic interferometry of crosscorrelation type, our results illustrate that the data-driven reflection imaging method based on seismic interferometry of cross-coherence type can automatically compress the band-limited source signature and make full use of background noise to broaden the bandwidth of reflection signals for achieving imaging results with a higher resolution.

Plasmaspheric Pi2 Pulsation Enhancement in Response to Plasma Sheet Pi2 Wave Source: Statistical Study Using Van Allen Probes and THEMIS Conjunctions

AbstractTo understand the enhancement of Pi2 pulsations inside the plasmasphere in response to the plasma sheet Pi2 wave source, we conduct a statistical investigation of 208 conjunction events by using simultaneous two‐point measurements with one satellite located in the plasmasphere and the other one located in the plasma sheet. All the events had a Pi2 compressional wave source observed in the plasma sheet as indicated by their association with bursty bulk flows (BBFs), but for about 25% of the events there were no corresponding enhancements in plasmaspheric Pi2 waves. For events with plasmaspheric Pi2 wave enhancements, a cavity or virtual resonance was likely the dominant wave mode, while excitation of field line resonance was also observed. We select two groups of events: strong (weak) group with the plasmaspheric compressional wave enhancements above 75% percentile (below 25% percentile), and conduct a statistical‐significance evaluation of the differences between the two groups. The strong events were observed closer to midnight than the weak events. The plasma sheet wave source that has a larger wave amplification or larger dipolarization associated with BBFs is more likely to excite stronger plasmaspheric wave enhancements. The strong events occurred more often with a pre‐condition of lower Auroral Electrojet (AE)* levels than did weak events. We explain these dependencies as strong events being associated with more favorable conditions that allow the inward‐propagating compressional waves from the plasma sheet wave source to reach the plasmapause and excite the plasmaspheric waves.

Forward modelling and identification of shallow gas in the Bohai Bay seabed

The accumulation of shallow gas in the seabed reduces the strength of strata or forms a high-pressure air sac, endangering ocean engineering construction. Therefore, it is important to identify the distribution of shallow gas in the seabed within the study area. Shallow gas increases the soil mass porosity and reduces the acoustic wave velocity, causing attenuation by absorbing to high-frequency components in the acoustic waves. Based on the geological drilling data in the area surrounding an oil platform in Bohai Bay, a stratigraphic model was established for forward analysis, and the results suggest the presence of the phase inversion of reflective waves at the interface between shallow gas and strata and sunken events for the lower shallow gas. According to a survey of stratigraphic profiles surrounding the platform, a seismic attribute analysis of acoustic stratigraphic profile data concerning amplitude, instantaneous phase, and instantaneous frequency was carried out, and characteristics such as disordered weak amplitude reflection, phase inversion, sunken events and indicators, including high-frequency loss and shallow gas reflection, were identified. Given that the shallow gas reflection is columnar and ended at the top clay strata of the seabed, the shallow gas was probably produced from deep depths.

A Historical Perspective of the La Niña Event in 2020/2021

AbstractEl Niño–Southern Oscillation is the strongest interannual variability in the tropical oceans and the major source of global climate predictability. In this work, we examine the evolution of oceanic and atmospheric anomalies in the tropical Pacific during 2020/2021 La Niña and compare it with the historical strong La Niña events since 1982, identify the contributions of different time scale components, and assess the predictions and the impact on extra‐tropical climate. 2020/2021 La Niña emerged in August 2020 and dissipated in May 2021. 2020/2021 La Niña was uniquely preceded by a borderline El Niño instead of an El Niño and a weak equatorial‐heat discharge process. That resulted in the weakest event among the strong La Niñas since 1982, although there were strong upwelling Kelvin wave activities. Moreover, compared with other strong La Niña events, the surface easterly wind anomalies and the warm pool extended further eastward in 2020/2021 La Niña, linking to a relatively weaker dipole‐like pattern of the subsurface ocean temperature anomalies. The strength of all the strong La Niña events is determined by the in‐phase amplification of all time scale variations. Their decay in the boreal spring and early summer is mainly controlled by the intra seasonal‐inter seasonal variation. 2020/2021 La Niña was successfully predicted, however, the North American climate anomalies did not match the typical La Niña response, leading to low prediction skill in the extra‐tropics during its mature phase.

Expansion of the seismological monitoring network on the Kola Peninsula

In July 2021, the seismological monitoring network of the Kola Branch of the Geophysical Survey of the Russia Academy of Sciences was expanded by installing a new seismic station. It is installed in the southern part of the Kola Peninsula in the village of Umba (station code UMBA). The expansion of the seismological network to the south has improved the monitoring detail of the Kandalaksha earthquake source zone. According to modern concepts, the Kolvitsky and Kandalaksha grabens are potentially the most seismically hazardous object in the eastern part of the Baltic Shield. To select the location of the new seismic station, reconnaissance work was carried out. This work included an assessment of the level of background seismic noise. The article presents an analysis of noise power spectral density for seismic station UMBA. A low level of background noise is shown in comparison with the NHNM and NLNM models. The following equipment is used at the seismic station: Guralp 6T analog seismometer (registration range 30 s - 50 Hz) and seismic signal recorder “Ermak-5”. Seismic data is transmitted in near real time to the Kola Regional Processing Center via mobile Internet channels. The ability to register weak seismic events with a local magnitude of less than 2 in the area of the Kandalaksha seismic zone and accurately determine the coordinates of their epicenters is shown by the example of a weak earthquake.

The Life Cycle and Variability of Antarctic Weak Polar Vortex Events

Abstract Motivated by the strong Antarctic sudden stratospheric warming (SSW) in 2019, a survey on the similar Antarctic weak polar vortex events (WPVs) is presented, including their life cycle, dynamics, seasonality, and climatic impacts. The Antarctic WPVs have a frequency of about four events per decade, with the 2002 event being the only major SSW. They show a similar life cycle to the SSWs in the Northern Hemisphere but have a longer duration. They are primarily driven by enhanced upward-propagating wavenumber 1 in the presence of a preconditioned polar stratosphere (i.e., a weaker and more contracted Antarctic stratospheric polar vortex). Antarctic WPVs occur mainly in the austral spring. Their early occurrence is preceded by an easterly anomaly in the middle and upper equatorial stratosphere in addition to the preconditioned polar stratosphere. The Antarctic WPVs increase the ozone concentration in the polar region and are associated with an advanced seasonal transition of the stratospheric polar vortex by about one week. Their frequency doubles after 2000 and is closely related to the advanced Antarctic stratospheric final warming in recent decades. The WPV-resultant negative phase of the southern annular mode descends to the troposphere and persists for about three months, leading to persistent hemispheric-scale temperature and precipitation anomalies. Significance Statement The Antarctic weak polar vortex events (WPVs) are similar to the sudden stratospheric warming (SSW), but many of their characteristics remain unclear. Their climatology is presented as a benchmark based on high-quality reanalysis datasets. WPVs have a life cycle that is similar to that of Arctic SSWs but has a longer duration. They occur due to the amplified tropospheric wave forcing in the presence of a preconditioned polar stratosphere. Its seasonality is partly controlled by the equatorial stratospheric easterly in addition to the polar stratosphere. Its occurrence is closely related to the advanced breakdown of the Antarctic polar vortex and can reduce the size of the Antarctic ozone hole. Moreover, it further causes persistent hemispheric-scale climate anomalies in the troposphere, which provides a prediction potential for surface weather and climate.

A high-resolution stalagmite record from Luoshui Cave, Central China over the past 23.5 kyr

A continuous high-resolution record from a precisely-dated stalagmite spanning the last precessional cycle provides new insight into the dynamics of climate change from orbital to centennial scales. A 600-mm length stalagmite (LS46) collected from the Luoshui Cave, Hubei Province, Central China, was well-dated (a total of 24 230Th dates) and high-resolved sampled for oxygen and carbon stable isotopic measurements (2047 subsamples in total). The stalagmite LS46 δ18O is consistent with other published stalagmite δ18O time series in monsoonal China, and closely tracks changes in the Northern Hemisphere summer insolation (NHSI) on July 21st throughout the past 23.5 kyr. Besides, the stalagmite LS46 δ18O shows significant correlations with the reconstructed Dali lake-level history and tree-ring δ18O records in the marginal monsoon regions. On this basis, we interpret that the stalagmite LS46 δ18O reflects the large-scale monsoon circulation with a superimposed local climate signal that might be related to effective humidity. Furthermore, the stalagmite LS46 δ18O exhibited four long-lasting extremely weak monsoon events since 7 kyr B.P.. These four weak monsoon events corresponded well with the tree-ring record in the northwestern fringe of the East Asian summer monsoon (EASM) region. Notably, the good correspondence between the stalagmite record and the tree-ring record also provides a good chronological support for our assessment of the climate and cultural evolution during the middle-late Holocene transition, the medieval warm period (MWP) and Little Ice Age (LIA). During the early-middle Holocene, the detrended δ18O profile revealed 10 multi-centennial monsoon cycles with a duration of nearly 500 yr and the amplitude of ∼0.8‰. The wavelet analysis further discloses that the EASM has nearly 500 yr and 200 yr periodic oscillations in the early-middle Holocene, research indicated that the solar activity and the North Atlantic Oscillation (NAO)/North Atlantic Deep Water (NADW) jointly drive the dominant nearly 500 yr cycle of the Asian monsoon.

Multicentennial to millennial–scale changes in the East Asian summer monsoon during Greenland interstadial 25

AbstractA multidecadal-resolved stalagmite δ18O record from two nearby caves, Lianhua and Dragon, in Shanxi Province, northern China, characterizes the detailed East Asian summer monsoon (EASM) intensity changes at 114.6–108.3 ka during Marine Oxygen Isotope Stage 5d. Our record shows an intensification of the EASM at 114.6–109.5 ka, followed by a rapid weakening at 109.5–108.4 ka. The millennial-scale strong monsoonal event appears to be correlated with the warm Greenland interstadial 25 (GI 25), whereas the weak monsoonal event is related to the cold Greenland stadial 25 within dating errors. The GI 25 monsoonal event registered in our record is also documented in various published time series from different regions of China. The lines of evidence indicate that this event occurred over the entirety of monsoonal China and was also broadly antiphase, similar to the corresponding event on a millennial time scale in the South American monsoon territory. In our record, one 700 yr weak monsoon event at 110.7+0.6−0.5 to 110.0+0.8−0.4 ka divides the GI 25 into three substages. These multicentennial to millennial–scale monsoon events correspond to two warm periods and an intervening cold interval for the intra-interstadial climate oscillations within GI 25, thus supporting a persistent coupling of the high- and low-latitude climate systems over the last glacial period.

Significant weak monsoon events during the early to middle Holocene transition: Pollen evidence from an alpine lake in North China

The response characteristics of East Asian summer monsoon (EASM) precipitation to abrupt climatic events during the early to middle Holocene transition may provide insights into the response of EASM precipitation to possible extreme climatic events under future global warming scenarios. We present a high-resolution (∼10 yr) pollen record from a hydrologically closed alpine lake (Yazihai Lake) in North China spanning the interval of 9000–7500 cal yr BP. The results reveal two significant weak monsoon events during 8830–8730 cal yr BP and 8100–8000 cal yr BP. Based on a comparison with the GRIP δ18O ice core record from Greenland and the stalagmite δ18O record from Dongge Cave in South China, we suggest that the second weak monsoon event (8100–8000 cal yr BP) recorded at Yazihai Lake corresponds to the 8.2 ka event that originated in the North Atlantic region, it is spatially and temporally synchronous between the northern and the southern parts of the EASM region and is characterized by a significant decrease in EASM precipitation. For the first weak monsoon event (8830–8730 cal yr BP) recorded at Yazihai Lake, it was also captured by pollen, stalagmite δ18O, and marine sedimentary records from middle to low latitudes of the Northern Hemisphere, and its nature and amplitude resemble the 8.2 ka event. We infer that the possible cause of these two significant weak monsoon events was related to the southward shift of the intertropical convergence zone (ITCZ) due to the collapse of the Atlantic Meridional Overturning Circulation (AMOC), triggered by meltwater influx to the North Atlantic Ocean, and that the abrupt climate signals were transmitted via the monsoon circulation from low latitudes to middle–high latitudes in the EASM region.

Nonlinear site response at liquefiable sites: Insights from downhole seismic observations

The nonlinear behavior of shallow soil plays an important role in modifying surface ground motions. We analyze the nonlinear site response at liquefiable sites using the compiled long-term ground motion data (ranging from 1992 to 2020 with over 2000 earthquake events) at four high-quality downhole arrays that have liquefied during at least one earthquake. Two nonlinear event parameters, the percentage of nonlinearity (PNL) and the frequency shift parameter (fsp), are used to quantify the modification of site response of strong events to that of weak events. Site-specific regression analyses are performed to correlate nonlinear event parameters to incident motion parameters. Results indicate that site response at liquefiable sites varies from linear to nonlinear to liquefied states as the incident motion intensity changes, and the occurrence of liquefaction could enhance the amplification of low-frequency and very-high-frequency ground motions. As strong-motion observations for liquefiable sites are very limited, the findings of this work are of significance for further study of strong-motion seismology at liquefiable sites.

An efficient diffraction stacking interferometric imaging location method for microseismic events

Migration-based location methods automatically obtain microseismic event locations without manual picking and often are used in microseismic monitoring during hydraulic fracturing. They use waveform stacking over all receivers to enhance the ability to detect weak events. However, these methods may fail to effectively increase the signal-to-noise ratio (S/N) of the stacked trace and may not obtain an accurate source location if polarity reversals occur in seismic records. To overcome this problem, traditional approaches rely on polarity correction by characteristic function or polarity determination by source moment-tensor inversion and focal mechanism search. To ensure location accuracy and efficiency, we have developed the diffraction stacking interferometric imaging (DSII) method for locating microseismic events. We first obtain the approximately symmetrical pattern responding to the source moment tensor by using diffraction stacking (DS) and then apply interferometric imaging to focus the pattern onto its center and extract the source location. The DSII method overcomes the inaccurate location problem under polarity reversal caused by source mechanisms, and it also benefits from the high efficiency and noise suppression of the DS. Moreover, the symmetrical pattern in the DS source image also can be used as a means of quality control for field data. We use synthetic and field data to demonstrate the location ability of this method. Our results indicate that the DSII can efficiently reduce the effects of strong noise on event detection and location. We can achieve a quasi-symmetrical pattern on the DS image and obtain a focused interferometric image when the velocity has systematic errors. Compared with the DS, the DSII method also has a better performance on sparse-receiver networks. Finally, the DSII method is applied to field data acquired using a surface array during hydraulic fracturing.

제100회 전국체육대회 및 제49회 세계선수권대회 평균대종목 연기내용 비교분석

The purpose of this study is to have a comparative analysis on performances of elite athletes in Korea and other countries in the balance beam event and suggest skills that Korean athletes need to learn first. This study targeted on 5 high school student athletes(KH) and 5 Korea Adult athletes(KA) who made to the finals at the 100th National Sports Festival and 5 athletes who made to the finals at the World Championship(WC). Then, this study analyzed the difficulty levels, scores, and connection score in mean(M), standard deviation(SD) and percentage(%). The results were as follows. First, all three groups preferred Difficulty D the most and performed Difficulty D 65 times among 120 skills. Only the elite athletes in Korea performed Difficulty A and Difficulty B while the elite athletes of other countries performed Difficulty G. Secondly, KH group showed mean start values of 5.020, mean execution scores of 7.207, and mean final scores of 12.247. KA group showed mean start values of 4.700, mean execution scores of 7.080, and mean final scores of 11.780. Mean while, WC group showed mean start values of 6.020, mean execution scores of 8.353, and mean final scores of 14.353. Third, KH group performed connection score 7 times with mean scores of 0.180 and KA group performed connection score 3 times with mean scores of 0.080. Mean while, WC group performed connection score 18 times and got the mean scores of 0.760. This study hopes to suggest the skills that Korean athletes need to learn first and be the basic data for improving the performance in the balance beam event which is regarded as one of the weak events.

Infrasonic, Acoustic and Seismic Waves Produced by the Axion Quark Nuggets

We advocate the idea that Axion Quark Nuggets (AQN) hitting the Earth can be detected by analysing the infrasound, acoustic, and seismic waves which always accompany their passage in the atmosphere and underground. Our estimates for the infrasonic frequency ν≃5 Hz and overpressure δp∼0.3 Pa for relatively large size dark matter (DM) nuggets suggest that sensitivity of presently available instruments is already sufficient to detect very intense (but very rare) events today with existing technology. A study of much more frequent but less intense events requires a new type of instrument. We propose a detection strategy for a systematic study to search for such relatively weak and frequent events by using distributed acoustic sensing and briefly mention other possible detection methods.

Diversity of ENSO‐Related Surface Temperature Response in Future Projection in CMIP6 Climate Models: Climate Change Scenario Versus ENSO Intensity

AbstractFew studies explore how the diversity of El Niño and Southern Oscillation (ENSO)‐related atmospheric response is influenced by anthropogenic forcing and ENSO intensity. We examine the diversity of surface temperature (Ts) anomalies related to weak, moderate and strong ENSO events in North America (NA) for present and future climates forced under four Shared Socioeconomic Pathways (SSP) scenarios in CMIP6 climate models. When ENSO intensity is weaker, the NA Ts anomalies are more sensitive/variable to different SSP scenarios than moderate and strong ENSO. The NA Ts anomalies are more sensitive to the impacts of ENSO intensity under a sustainable climate change scenario, compared to the high SSP scenario. We discuss why the diversity of ENSO‐related Ts response projections differs in the combination of ENSO intensity and climate change scenarios.

Turbidity currents on the open slope of the Fraser Delta

Turbidity currents have been observed and measured in submarine channels and canyons where the flows are confined, but with the exception of one serendipitous direct measurement, are only inferred to occur on unconfined delta slopes. In this paper, direct measurement of turbidity currents on the Fraser delta slope are reported and their dynamics compared to turbidity currents in channelized settings. Twelve turbidity current events occurring between May 2014 and June 2018 were identified from Acoustic Doppler Current Profiler instruments deployed at two sites (109 and 159 m water depth). All the events occurred in the months of May and June, in association with high spring river flow. Five of the events were recorded at both sites and the timing of first arrivals gives estimates of the current speed ranging from 0.4 to 3.6 m s−1. Direct current measurements confirm that most flow speeds exceed 1.5 m s−1, although one weak event did not exceed 0.4 m s−1. Current profiles indicate that the flows are of variable thickness, ranging from less than 3 m to 15 m. The turbidity current events varied in duration from 5 to 66 min and, in the cases where transit speeds were available, the durations were proportionally shorter when the transit speed was high. In stronger flows, the initial stage of the flow is highly variable, suggesting extreme turbulence, and the velocity structure of the flow is similar to previous experimental and field observations, with a distinctive relatively thin, high speed lower region being evident at times. Downslope translation of the instrument platform during two of the events suggest the presence of a dense basal layer up to 2.75 m thick, as suggested in the travelling wave model of Heerema et al. (2020). The fact that only approximately half the flows measured at the shallower site are observed at the deeper site suggest that the runout distances of open slope flows are limited. Weaker flows are barely distinguishable in speed and direction from ambient tidal velocities. Flow directions suggest that the open slope flows are unconfined and initiate in the upper slope area that is approximately the same as the area of upslope sediment waves. It is hypothesized that shallow gullies in the same area may be important for initiation and ignition of the flows that become unconfined on the lower part of the slope.