Geology topics

Mengjie Wei

Publications and source records attributed to Mengjie Wei.

3 recordsLinked to original sources

USGS2020

The community code verification exercise for simulating sequences of earthquakes and aseismic slip (SEAS)

Numerical simulations of sequences of earthquakes and aseismic slip (SEAS) have made great progress over past decades to address important questions in earthquake physics. However, significant challenges in SEAS modeling remain in resolving multiscale interactions between earthquake nucleation, dynamic rupture, and aseismic slip, and understanding physical factors controlling observables such as seismicity and ground deformation. The increasing complexity of SEAS modeling calls for extensive efforts to verify codes and advance these simulations with rigor, reproducibility, and broadened impact. In 2018, we initiated a community code-verification exercise for SEAS simulations, supported by the Southern California Earthquake Center. Here, we report the findings from our first two benchmark problems (BP1 and BP2), designed to verify different computational methods in solving a mathematically well-defined, basic faulting problem. We consider a 2D antiplane problem, with a 1D planar vertical strike-slip fault obeying rate-and-state friction, embedded in a 2D homogeneous, linear elastic halfspace. Sequences of quasi-dynamic earthquakes with periodic occurrences (BP1) or bimodal sizes (BP2) and their interactions with aseismic slip are simulated. The comparison of results from 11 groups using different numerical methods show excellent agreements in long-term and coseismic fault behavior. In BP1, we found that truncated domain boundaries influence interseismic stressing, earthquake recurrence, and coseismic rupture, and that model agreement is only achieved with sufficiently large domain sizes. In BP2, we found that complexity of fault behavior depends on how well physical length scales related to spontaneous nucleation and rupture propagation are resolved. Poor numerical resolution can result in artificial complexity, impacting simulation results that are of potential interest for characterizing seismic hazard such as earthquake size distributions, moment release, and recurrence times. These results inform the development of more advanced SEAS models, contributing to our further understanding of earthquake system dynamics.

Seismological Research Letters↗

USGS2019

A 3-year in-situ measurement of CO2 efflux in coastal wetlands: Understanding carbon loss through ecosystem respiration and its partitioning

Understanding the link between ecosystem respiration (Reco) and its influential factors is necessary to evaluate the sources of gaseous carbon loss in coastal wetlands. Seablite (Suaeda salsa Pall.) is the main vegetation type pioneering temperate coastal wetlands in northeast China, and is generally an understudied wetland type. To evaluate the influence of environmental factors on Reco, a multi-year in-situ experiment was carried out during the growing seasons of 2012 to 2014. Total CO2 efflux was measured and separated further into soil microbial and belowground root respiration (Rs + r) and plant respiration (Rplant). Reco displayed strong seasonal variation, with effluxes as high as 845 to 1150 mg CO2 m−2 h−1 during summer months and as low as 32 to 111 mg CO2 m−2 h−1 during spring (when new shoots are sprouting) and fall (when plants are senescing) months. Aboveground plant structures contributed on average 79% to total plant biomass, and accounted for most of the Reco measured; i.e., 62–96% was associated as Rplant. Plant activity was strongly seasonal, accordingly driving Reco, with 1 g of soil-emergent S. salsa biomass (dry weight) producing approximately 1.58 mg CO2 per hour toward Reco during mid-summer. When water level was below the soil surface, Rs + r was exponentially correlated to air temperature. Because Reco for S. salsa marsh in the Liaohe Delta is controlled by plant growth cycles, inundation regime, and air temperature, this finding may be applied for national carbon budget estimation purposes from S. salsa wetlands throughout Northeast China and potentially close a key gap in understanding the role of this large wetland area in contributing to respiratory CO2 emissions globally.

Wetlands↗

USGS2016

Inter-annual variability of area-scaled gaseous carbon emissions from wetland soils in the Liaohe Delta, China

Global management of wetlands to suppress greenhouse gas (GHG) emissions, facilitate carbon (C) sequestration, and reduce atmospheric CO 2 concentrations while simultaneously promoting agricultural gains is paramount. However, studies that relate variability in CO 2 and CH 4 emissions at large spatial scales are limited. We investigated three-year emissions of soil CO 2 and CH 4 from the primary wetland types of the Liaohe Delta, China, by focusing on a total wetland area of 3287 km 2 . One percent is Suaeda salsa , 24% is Phragmites australis , and 75% is rice. While S . salsa wetlands are under somewhat natural tidal influence, P . australis and rice are managed hydrologically for paper and food, respectively. Total C emissions from CO 2 and CH 4 from these wetland soils were 2.9 Tg C/year, ranging from 2.5 to 3.3 Tg C/year depending on the year assessed. Primary emissions were from CO 2 (~98%). Photosynthetic uptake of CO 2 would mitigate most of the soil CO 2 emissions, but CH 4 emissions would persist. Overall, CH 4 fluxes were high when soil temperatures were >18°C and pore water salinity <18 PSU. CH 4 emissions from rice habitat alone in the Liaohe Delta represent 0.2% of CH 4 carbon emissions globally from rice. With such a large area and interannual sensitivity in soil GHG fluxes, management practices in the Delta and similar wetlands around the world have the potential not only to influence local C budgeting, but also to influence global biogeochemical cycling.

Liaohe Delta↗