Fluids Triggered the 2021 Mw 6.1 Yangbi Earthquake at an Unmapped Fault: Implications for the Tectonics at the Northern End of the Red River Fault

On 21 May 2021 a magnitude Mw 6.1 earthquake occurred in Yangbi region, Yunan, China, which was widely felt and caused heavy casualties. Imaging of the source region was conducted using our improved double-difference tomography method on the huge data set recorded by 107 temporary stations of ChinArray-I and 62 permanent stations. Pronounced structural heterogeneities across the rupture source region are discovered and locations of the hypocenters of the Yangbi earthquake sequence are significantly improved as the output of the inversion. The relocated Yangbi earthquake sequence is distributed at an unmapped fault that is almost parallel and adjacent (∼15 km distance) to the Tongdian–Weishan fault (TWF) at the northern end of the Red River fault zone. Our high-resolution 3D velocity models show significant high-velocity and low-VP/VS ratios in the upper crust of the rupture zone, suggesting the existence of an asperity for the event. More importantly, low-VS and high-VP/VS anomalies below 10 km depth are imaged underlying the source region, indicating the existence of fluids and potential melts at those depths. Upward migration of the fluids and potential melts into the rupture zone could have weakened the locked asperity and triggered the occurrence of the Yangbi earthquake. The triggering effect by upflow fluids could explain why the Yangbi earthquake did not occur at the adjacent TWF where a high-stress accumulation was expected. We speculate that the fluids and potential melts in the mid-to-lower crust might have originated either from crustal channel flow from the southeast Tibet or from local upwelling related to subduction of the Indian slab to the west.

Recharge mechanism and salinization processes in coastal aquifers in Nam Dinh province, Vietnam

In Nam Dinh province, in the Red River delta plain in Northern Vietnam, groundwater in the shallow Holocene aquifer shows elevated total dissolved solids up to 35 km from the coastline, indicating a saltwater intrusion from the Gulf of Tonkin. High groundwater salinities have been encountered below and adjacent to the Red River in the deep Pleistocene aquifer. Since 1996, large-scale groundwater abstraction was initiated from the deep aquifer, and the observed elevated salinities now raise concerns about whether the groundwater abstraction is undertaken sustainably. We have conducted a study to obtain a fundamental understanding of the recharge mechanisms and salinization processes in the Nam Dinh province. A holistic approach with multiple methods including transient electromagnetic sounding and borehole logging, exploratory drilling, sampling and analyzing primary ion and stable isotope compositions of water and pore water, groundwater head monitoring, hydraulic experiments laboratory of clay layers, and groundwater modeling by using the SEAWAT code. Results reveal that saline river water is leached from the Red River and its distributaries into the shallow aquifers. The distribution and occurrence of salty pore water in the Holocene aquitard clay shows that meteoric water has not been flowing through these low permeable clay layers. Marine pore water has, however, been leached out of the Pleistocene clay. When this layer is present, it offers protection of the lower aquifer against high salinity water from above. Salinity as high as 80 % of oceanic water is observed in interstitial pore water of the transgressive Holocene clay. Saltwater is transported into the Pleistocene aquifer, where the Holocene clay is directly overlying the aquifer.

Zoning groundwater potential recharge using remote sensing and GIS technique in the Red river delta plain

The Red River delta plain is the second largest delta in Vietnam and is located in the North of the country with an area of 14,860 km2 and residing more than 22.5 million inhabitants. Groundwater is mainly exploited in Quaternary sedimentary aquifers with a total discharge of about 3 million m3/day. Some localities have shown signs of over-exploitation such as in Hanoi and in Nam Dinh, which may lead to related problems such as depletion, subsidence, saltwater intrusion, and water pollution. In order to be able to sustainably exploit groundwater, the groundwater potential recharge needs to be estimated. There have been many studies using different methods to estimate the groundwater recharge and to zone potential recharge. In the study area, there are several studies for groundwater recharge, but some are still uncertain because of using indirect methods, some are locally estimated in specific areas. Therefore, the objective of this study is to apply remote sensing and GIS to zone the groundwater potential recharge and its verification by using radioactive isotope 3H analysis in the Red River delta plain. Various types of satellite images have been used and interpreted to detect the different thematic layers which concern the groundwater potential recharge. GIS has been applied as a platform for analysis and integration of thematic layers for zonation, finally. Field trip and water sampling for chemical and radioactive 3H analysis were also conducted. Zones with low, moderate, and high groundwater potential recharge have been delineated with good agreement from the direct estimation of groundwater recharge by radioactive isotopes 3H.

APPLICATION OF HIGH-TECH AGRICULTURE BY HOUSEHOLDS IN THE RED RIVER DELTA OF VIETNAM

This study is conducted to model the factors that influence the decision to apply high technology in agricultural production (agricultural production) of farmers in the Red River Delta (RRD), Vietnam. Data used for the study are surveyed in fact 600 households participating in agricultural production in the RRD. The paper uses the Binary Logistic regression analysis method to identify the factors affecting the decision to apply high technology to agricultural production. The research results show that factors such as farm households' education, people's participation in social organizations, the impact of urbanization, capital and market availability all have positive effects extreme decision to apply technology of farmers. Based on the results of the study, the paper proposed policies to be focused on to enhance the application of high technology in agricultural production by farmers. The findings of this study demonstrate that people's application of high technology to agricultural production is improved by enhancing their production capacity.

Outdoor Recreation and Rural Transitions in Central Appalachia: Revisiting the Economic Impact of Rock Climbing in Kentucky’s Red River Gorge

Kentucky’s Red River Gorge is a popular rock climbing destination located amid longstanding poverty in America’s Central Appalachian region. Climbing represents an important part of the outdoor recreation economy and may provide one alternative to mono-economic extractive industry dependency in this region. This study examines the economic impact of climbing in the Red utilizing an online survey of rock climbers and economic impact methodology. The survey examines expenditures in lodging, food purchases, travel, retail purchases, and services. The survey also collected visitation and demographics data. The authors estimate climbers spend $8.7 million annually (up from $3.8 million in 2015) and support over 100 jobs in some of the poorest counties in the region and nation. The study reiterates previous findings indicating climbers are well-educated with incomes higher than those typically found in this region. The study’s results help reframe the value of climbing’s economic impact in rural transitional economies throughout Central Appalachia. These findings also raise policy implications regarding public land access and reducing climber environmental impacts on public lands.

Vietnam labour policies and its impact on rural wages: an experience from hired farm labourers in the Red River Delta

Purpose. The purpose of this article is to understand how Vietnamese policies for labour impacting on wage of rural labourers in agricultural sector. To do that, the paper particularly pays attention on analyzing wage of hired farm labourers in the Red River Delta region, the rice basket of Vietnam. Methodology / approach. Analyzing the above-mentioned impact of Vietnamese policies was performed by using data surveyed from 150 hired farm labourers in the Red River Delta of Vietnam. The survey on wages of rural labourers was conducted in Bac Ninh, Thai Binh and Hai Duong which are the three typical agricultural production areas in the Red River Delta in 2019. In this survey, the author interviewed 150 people who work as hired labourers in rice cultivation in Bac Ninh, clam farming in Thai Binh and pig raising in Hai Duong. The sample was randomly drawn among farm households which hire labourers in these provinces. This sample was divided into 2 groups of female and male labourers. The main purposes of this survey were to gather both qualitative and quantitative data on hired labourers including: age, gender, education level, money wage, wage in kind and other remunerations that they received from employers. Information relating to their participation in social insurance and vocational training were also collected like: number of years involving in social insurance; money that they used to purchase social insurance; frequency and time spending in vocational training courses. The personal interviews using a standard questionnaire with open and close questions were implemented separately with male and female hired farm labourers. They were interviewed in different places to ensure that their responses do not affect others. After checking for missing values, the author used the following methods: frequency distribution with mean and standard deviation for a description of respondents; cross tabulation and T-test were also used to test for differences in proportions and significant difference between groups; a linear regression model was applied to examine impact of wage regulation, social insurance and vocational training policies on wage of hired labourers in agricultural production (dependent variable was average money wage per month, it was estimated by sum of money wage and other remunerations that a labourer gets each month; independent variables were age, gender, education level and dummy variables which represented labourers’ participation in mentioned labour policies). Results. Among policies relating to agricultural sector, the ones about minimum wage and vocational training statistically impact the most on labour wage. Longer time of vocational training brings an additional 3 USD to a labourer’s monthly wage. Being supported by the policy of minimum wage, labourers can achieve higher wage when negotiating with employers. The author found that wage of a labourer who is aware of this policy is about 5 USD higher than that of others. Meanwhile, social insurance policies do not impact on wage of rural farm labourers. It is stated in the Labour Code that a part of social insurance fee of a contracted labourer is paid by his/her employer. However, hired agricultural labourers usually are excluded, because they mostly work under verbal agreements which are not specified by the Code. This loophole in the Labour Code need to be corrected in the future. Originality / scientific novelty. Despite the fact that industrialization process is rapidly developing in recent years, rural labour force still contributes a remarkable proportion in the Red River Delta region of Vietnam. The transferring skilled and young labourers from farm to off-farm sectors, from rural to urban areas leads to the existence of un-skilled and old-age labourers for agricultural production. This labour force is working in the poor condition with unstable and low wage jobs. However, they are not much concerned by labour policies and there is still a gap in research on their wage. Therefore, this study takes the advance to shed the light on the impact of labour policies on wage of rural farm labourers as well as to propose recommendations to adjust labour policies regarding this issue. Practical value / implications. The author identifies that attending vocational training and understanding of minimum wage will increase the chance for labourers to obtain higher wage.