Earthquake Disturbance Research Articles

A Growth-Survival Trade-Off Along an Elevation Gradient Is Altered by Earthquake Disturbance in a Monodominant Southern Beech Forest.

Tree growth-survival relationships link two demographic processes that individually dictate the composition, structure and functioning of forest ecosystems. While these relationships vary intra-specifically, it remains unclear how this reflects environmental variation and disturbance. We examined the influence of a 700-m elevation gradient and an Mw = 6.7 earthquake on intra-specific variability in growth-survival relationships. We expected that survival models that incorporated recent growth would be better supported than those only using other factors known to influence tree survival. We used a permanent plot network that representatively sampled a monodominant Nothofagus forest in New Zealand's Southern Alps in 1974 and that was remeasured seven times through to 2009. The relationships were assessed using pre-earthquake growth and survival, pre-earthquake growth and post-earthquake survival (0-5 years post-earthquake), and post-earthquake growth and survival (5+ years post-earthquake). Survival was related to growth of 4504 trees on 216 plots using Bayesian modelling. We hypothesised there would be a positive, logistic relationship between growth and survival. Pre-earthquake, we found a positive, logarithmic growth-survival relationship at all elevations. At higher elevations, trees grew more slowly but had higher survival than trees at lower elevations, supporting our hypothesised demographic trade-off with elevation. The earthquake altered growth-survival relationships from those found pre-earthquake and 0-5 years post-earthquake survival held little relationship with growth. A strong, logarithmic growth-survival relationship developed 5+ years post-earthquake because of enhanced survival of fast-growing trees yet low survival of slow-growing trees. Synthesis. Our findings demonstrate a trend in growth-survival relationships along an elevation gradient. If we assume a gradual climate warming is the equivalent of a forest stand shifting to a lower elevation, then data from our pre-earthquake period suggest that tree growth-survival relationships at any elevation could adjust to faster growth and lower survival. We also show how these novel growth-survival relationships could be altered by periodic disturbance.

Spatio-temporal variation and influencing factors of ecol-environment quality in Jiuzhaigou County, Sichuan, China under seismic disturbance.

Accurately monitoring and evaluating changes in ecological environment quality under earthquake disturbances is of great significance for the restoration and protection of regional ecological environment. In view of the "8·8" earthquake in Jiuzhaigou County in 2017, we used high-precision remote sensing image to analyze the vege-tation damage caused by the earthquake, and calculated remote sensing ecological index (RSEI) for the pre-earthquake period, post-earthquake period and 3-year recovery period based on GEE platform to analyze the spatio-temporal variation of ecological environment in Jiuzhaigou County, Sichuan Province. Then, we used geodetector to reveal the influencing factors of spatio-temporal variations in ecological restoration. The results showed that the fractional vegetation cover of Jiuzhaigou County decreased from 0.71 before the earthquake to 0.69 after the earthquake. The area of higher coverage zone decreased by 310.78 km2, while the area of others increased. The mean RESI decreased from 0.50 in the pre-earthquake period to 0.42 in the post-earthquake period, and increased to 0.50 after the 3-year recovery period. The ecological environment quality in the three period was mainly at the good and ave-rage levels, and it was distributed in the central and southern mountains and the eastern river valley. Annual precipitation, elevation, wet and greenness were the main factors controlling ecological quality restoration in Jiuzhaigou County, and the increases in the interaction among these factors would affect the spatial variations of regional ecological environment quality restoration.

Investigation of Atmospheric Anomalies due to the Great Tohoku Earthquake Disturbance Using NRLMSISE-00 Atmospheric Model Measurement

In this study, the atmospheric changes for the 9.0-magnitude Tohoku earthquake, which occurred on March 11, 2011, are analyzed. The March 11, 2011 earthquake was preceded by a large foreshock on March 09, 2011 with magnitude M 7.3 and depth 32 km at 02:45:20 UT near the east coast of Honshu, Japan. The earthquake doesn’t limit its effects on the Earth’s lithosphere, hydrosphere and biosphere; it also extends its effects to the atmosphere because of the gas emissions, which produce large-scale seismic waves from the ground and release gases into the atmosphere. In this study, the anomalies of the atmospheric parameters are studied by using one of the atmospheric models from the Naval Research Laboratory Mass Spectrometer Incoherent Scatter Extension 2000 (NRLMSISE-00) model data to analyze the atmospheric anomalies of the Tohoku Earthquake on March 11, 2011. The atmospheric parameters of atomic oxygen (O), hydrogen (H), atomic nitrogen (N), helium (He), argon (Ar), molecular oxygen (O2), molecular nitrogen (N2), total mass density (ρ), neutral temperature (Tn), exospheric temperature (Tex) and anomalous oxygen (AO) are used for analysis during the earthquake occurrence. The epicenter of the Tohoku earthquake, with a geographical location of latitude 38.30° N and longitude 142.37° E, is used for the NRLMSISE-00 model as input parameters to analyze the output of atmospheric parameters. To compare the atmospheric changes caused by the earthquake, 5 days before and after the earthquake are considered. To detect where the atmospheric parameters increased or decreased from the earthquake day, the percentage deviation of the NRLMSISE-00 model is applied. The results indicate that there were atmospheric parameter anomalies that occurred a few days before, following and during the earthquake on March 11, 2011. Except for hydrogen (H), all atmospheric parameters average daily percentage deviation values were positive during the 5 days before and after with respect to the main earthquake shock on March 11, 2011. The NRLMSISE-00 model can capture the atmospheric parameter anomalies of the Tohoku earthquake well.

Forest Resilience in the Himalayas Inferred From Tree Growth After Earthquake Disturbances

AbstractThe Himalayas are one of the most seismically active regions in the world; thus, experiencing frequent catastrophic earthquakes. A growing body of evidence has shown that large earthquakes severely impact on forest ecosystems, particularly in mountain regions. However, little is known about the impact of severe earthquakes on Himalayan forests. Herein, we analyzed tree radial growth patterns following major earthquakes that occurred in 1833, 1905, 1916, 1934, and 1936 in the Himalayas. Based on 46 tree‐ring sites, 77%, 64%, 73%, 72%, and 77% of total analyzed trees showed responses to these seismic events, respectively. On average, 72% of responsive trees undergo growth suppressions following the earthquake events. Superposed epoch analysis showed a strong growth decline 1–5 years after the earthquake. A negative relationship was found between the percentage of responsive trees and the distance of the tree‐ring site from the earthquake's epicenter. The mean time required for 75% of trees to recover reached 5, 5, 5, 13, and 28 years following the earthquake of 1833, 1905, 1916, 1934, and 1936, respectively. The recovery time after a low growth period showed a negative relationship with the distance to earthquake's epicenter. However, the growth resistance improved with increasing distance from the epicenter. Thus, forests located close to earthquakes' epicenters can serve as reliable archive for the reconstruction of earthquakes' impacts. As the Himalayas are prone to earthquakes, adaptive management strategies are required to minimize the impacts of earthquakes on the mountain forest ecosystem.

Increased nonstationarity of stormflow threshold behaviors in a forested watershed due to abrupt earthquake disturbance

Abstract. Extreme earthquake disturbances to the vegetation of local and regional landscapes could swiftly impair the former hydrologic function, significantly increasing the challenge of predicting threshold behaviors of rainfall–runoff processes as well as the hydrologic system's complexity over time. It is still unclear how alternating catchment hydrologic behaviors under an ongoing large earthquake disruption are mediated by long-term interactions between landslides and vegetation evolution. In a well-known watershed affected by the Wenchuan earthquake, the nonlinear hydrologic behavior is examined using two thresholds with intervening linear segments. A lower rising threshold (THr) value (210.48 mm) observed in post-earthquake local landslide regions exhibited a faster stormflow response rate than that in undisturbed forest and grassland–shrubland regions, easily triggering huge flash-flood disasters. Additionally, an integrated response metric pair (integrated watershed average generation threshold THg−IWA and rising threshold THr−IWA) with areas of disparate land use, ecology, and physiography was proposed and efficiently applied to identify emergent catchment hydrologic behaviors. The interannual variation in the two integrated hydrologic thresholds before and following the earthquake was assessed to detect the temporal nonstationarity in hydrologic extremes and nonlinear runoff response. The year 2011 was an important turning point along the hydrologic disturbance–recovery timescale following the earthquake, as post-earthquake landslide evolution reached a state of extreme heterogeneity in space. At that time, the THr−IWA value decreased by ∼ 9 mm compared with the pre-earthquake level. This is closely related to the fast expansion of landslides, leading to a larger extension of variable source area from the channel to neighboring hillslopes, and faster subsurface stormflow, contributing to flash floods. Finally, we present a conceptual model interpreting how the short- and long-term interactions between earthquake-induced landslides and vegetation affect flood hydrographs at event timescale that generated an increased nonstationary hydrologic behavior. This study expands our current knowledge of threshold-based hydrologic and nonstationary stormflow behaviors in response to abrupt earthquake disturbance for the prediction of future flood regimes.

Study on co-seismic ionospheric disturbance of Alaska earthquake on July 29, 2021 based on GPS TEC

With the rapid development of space geodetic information technology, the Global Positioning System (GPS) has been widely used in seismology and space environmental research. Typically, the occurrence of a large earthquake will lead to some changes in the ionosphere, this phenomenon is called coseismic ionospheric disturbances (CIDs). In this contribution, differential slant total electron content (dSTEC) is used to study the anomalous characteristics of the ionosphere. First, based on the ionospheric dSTEC time series and two-dimensional disturbance detection, the temporal and spatial characteristics of ionospheric disturbances can be accurately analysed. Secondly, using wavelet transform spectrum analysis and disturbance propagation velocity, it can be determined that the disturbance sources of this earthquake can be identified as acoustic wave, gravity wave and Rayleigh wave. Finally, in order to further clarify the direction of the earthquake disturbance, this study focuses on proposing an innovative method for the disturbance propagation direction, and determines that there are two directions of the propagation of the CIDs of the Alaski earthquake.

Earthquake disturbance shifts metabolic energy use and partitioning in a monodominant forest

AbstractAimBoth macroecology and disturbance ecology have long been used to characterize population‐ and community‐level patterns across scales, but the integration of both approaches in characterizing disturbed ecosystems is rare. Here, we use the maximum entropy theory of ecology (METE) to model the individual size distribution (ISD) of trees in pre‐ and post‐disturbance tree populations and estimate the corresponding metabolic scaling exponents.LocationNew Zealand.Time Period1987–1999.Major Taxa StudiedMountain beech (Fuscospora cliffortioides Nothofagaceae).MethodsMETE uses information entropy and empirical macro‐state variables to constrain predictions of ecological distributions related to biodiversity. METE has successfully predicted a range of biodiversity metrics in static or relatively undisturbed conditions. However, METE can fail to accurately model ecological patterns in disturbed ecosystems. We extend existing theoretical predictions to a highly disturbed ecosystem by treating the metabolic scaling exponent and Lagrange multipliers as free parameters in METE.ResultsWe showed that the fully parameterized METE (FP‐METE) model reasonably predicted the ISD of mountain beech populations in a monodominant forest after a strong earthquake, which restructured the forest. Furthermore, the FP‐METE model revealed that decreasing metabolic scaling exponent drove the substantial decline of total metabolic rate energy and the redistribution of energy towards smaller trees after the earthquake. Increased number of small trees was not sufficient to capture the full impact of disturbance on forest energy use.Main ConclusionsOur FP‐METE model applies an informatics approach to estimate the metabolic scaling relationship. We find that instead of maintaining a fixed value, the metabolic scaling exponent is variable among populations, and declines significantly after an earthquake disturbance. This leads to major shifts in the total population metabolic energy and energy distribution. With this approach, we now have the opportunity to advance beyond categorizing forms of mathematical distributions that describe biodiversity patterns and move into a predictive framework where the true constraints on ecosystems and their dynamics emerge.

Influence of earthquake disturbance on concrete strength at early age

Construction projects commonly run for years in earthquake zones always have certain seismic risks during the construction process. For early-age concrete that has not fully reached the design strength, whether earthquake action will affect its final strength, and to what extent, needs to be studied. This paper experimentally studied the influence of earthquake on final strength of concrete of grade C30 and C35 with earthquake simulation shaking table at the curing age of 3 h (h) and 8 h (h). Seismic wave speed of 0.1g, 0.2g, 0.3g, 0.4g, 0.5g was applied to the test blocks except for control specimens. After being disturbed by the earthquake at the age of 3h, it still has certain fluidity and can be well recovered by hydration process, hence the strength reduction is less than 4%. In contrast, at the age of 8h, the concrete block is in the final setting stage and become a solid state. After being disturbed by earthquakes, the compressive strength of these specimens has a significant decrement trend compared to the control specimen. Based on the findings, concrete at initial setting stage is less affected by seismic wave. While the seismic wave speed has a more obvious effect on the final strength for concrete at the final setting stage, i.e. when peak acceleration disturbance is greater than 0.4g. It was also observed that the final strength decreases with the increase of the acceleration peak value.

Parallel recolonizations generate distinct genomic sectors in kelp following high-magnitude earthquake disturbance.

Large‐scale disturbance events have the potential to drastically reshape biodiversity patterns. Notably, newly vacant habitat space cleared by disturbance can be colonized by multiple lineages, which can lead to the evolution of distinct spatial “sectors” of genetic diversity within a species. We test for disturbance‐driven sectoring of genetic diversity in intertidal southern bull kelp, Durvillaea antarctica (Chamisso) Hariot, following the high‐magnitude 1855 Wairarapa earthquake in New Zealand. Specifically, we use genotyping‐by‐sequencing (GBS) to analyse fine‐scale population structure across the uplift zone and apply machine learning to assess the fit of alternative recolonizaton models. Our analysis reveals that specimens from the uplift zone carry distinctive genomic signatures potentially linked to post‐earthquake recolonization processes. Specifically, our analysis identifies two parapatric spatial‐genomic sectors of D. antarctica at Turakirae Head, which experienced the most dramatic uplift. Based on phylogeographical modelling, we infer that bull kelp in the Wellington region was probably a source for recolonization of the heavily uplifted Turakirae Head coastline, via two parallel, eastward recolonization events. By identifying multiple parapatric genotypic sectors within a recently recolonized coastal region, the current study provides support for the hypothesis that competing lineage expansions can generate striking spatial structuring of genetic diversity, even in highly dispersive taxa.

Evaluating resiliency of electric power generators against earthquake to maintain synchronism

Natural disasters, such as earthquakes, can cause significant disruptions in power systems, such as loss of generations and loads. To evaluate the behavior of a generator to remain in synchronism, subjected to the large disturbance of an earthquake, we propose a dynamic generator resiliency model. The proposed approach models the effects of earthquake energy transfer to a generator considering the time-variant behavior of earthquake disturbance. In addition, the proposed model analyzes the transient behavior of generators impacted by an earthquake considering earthquake ground acceleration and generators’ dynamic characteristics. Using this model, we can determine synchronism status of impacted generators and transient stability status of a power system in response to an earthquake. The proposed approach is tested using real-world data including the data of a real earthquake occurred on a real power plant. The obtained results illustrate the effectiveness of the proposed model to correctly predict the impact of an earthquake on a power plant, and to determine the effects of earthquake magnitude and generator robustness (in terms of generator inertia and damping torque) on the response of a generator to an earthquake.

The mechanism of slope instability due to rainfall-induced structural decay of earthquake-damaged loess

Natural loess slopes are characterized by a strong geological structure, which is an important factor in maintaining slope stability. The magnitude and duration of the earthquake may disturb the soil structure at different levels degrees, locally changing the arrangement between soil particles. The process of rainfall humidification weakens the cementation between soil particles, and the disturbance and humidification change the structural state of the soil, which in turn causes sliding of the slope along with the decay of soil mechanical properties. As slope instability is often the result of a series of post-earthquake ripple effects, it is of great scientific significance to study the mechanism of slope instability due to the structural decay of earthquake-damaged loess exacerbated by rainfall. In this paper, the impact of structural decay of loess on slope stability is simulated by GEOSTUDIO software under three conditions: pre-earthquake rainfall, post-earthquake rainfall and earthquake, taking the landslide in Buzi Village, Min County, Gansu Province as an example. The comparative analysis of the calculation results shows that the structural properties of the slope without earthquake disturbance are influenced by infiltration amount. When it is fully saturated, the structural properties are similar to those of saturated soil, and the safety factor is reduced by 12.9%. In addition, the earthquake intensity and duration have different degrees of structural damage to the soil. When the structure is fully damaged, it is similar to that of remodelled soil, and the safety factor is reduced by 45.84%. Notably, the process of the earthquake and the following humidification generates the most serious damage to the loess structure, with a reduction in the safety factor of up to 56.15%. The quantitative analysis above obviously illustrates that the post-earthquake rainfall causes the most severe damage to structural loess slopes, and the resulting landslide hazard should not be underestimated.

Concordant phylogeographic responses to large-scale coastal disturbance in intertidal macroalgae and their epibiota.

Major ecological disturbance events can provide opportunities to assess multispecies responses to upheaval. In particular, catastrophic disturbances that regionally extirpate habitat-forming species can potentially influence the genetic diversity of large numbers of codistributed taxa. However, due to the rarity of such disturbance events over ecological timeframes, the genetic dynamics of multispecies recolonization processes have remained little understood. Here, we use single nucleotide polymorphism (SNP) data from multiple coastal species to track the dynamics of cocolonization events in response to ancient earthquake disturbance in southern New Zealand. Specifically, we use a comparative phylogeographic approach to understand the extent to which epifauna (with varying ecological associations with their macroalgal hosts) share comparable spatial and temporal recolonization patterns. Our study reveals concordant disturbance-related phylogeographic breaks in two intertidal macroalgal species along with two associated epibiotic species (a chiton and an isopod). By contrast, two codistributed species, one of which is an epibiotic amphipod and the other a subtidal macroalga, show few, if any, genetic effects of palaeoseismic coastal uplift. Phylogeographic model selection reveals similar post-uplift recolonization routes for the epibiotic chiton and isopod and their macroalgal hosts. Additionally, codemographic analyses support synchronous population expansions of these four phylogeographically similar taxa. Our findings indicate that coastal paleoseismic activity has driven concordant impacts on multiple codistributed species, with concerted recolonization events probably facilitated by macroalgal rafting. These results highlight that high-resolution comparative genomic data can help reconstruct concerted multispecies responses to recent ecological disturbance.

Influence of Mine Earthquake Disturbance on the Principal Stress of the Main Roadway near the Goaf and Its Prevention and Control Measures

With the reduction and depletion of shallow energy, the mining depth of coal around the world is increasing year by year, and the mining depth of some coal mines in China has reached kilometers. The main roadway near the goaf with the deep high static stress is very easy to be damaged after being disturbed by the mine earthquake. Taking the main roadway in the no. 1 mining area of Gaojiapu coal mine in Binchang mining area, Shaanxi Province, China, as the engineering background, the high-energy mine earthquake monitored by the on-site microseism is equivalently simulated through the dynamic module of FLAC3D, and the spatial-temporal rotation characteristics of the principal stress of roadway surrounding rock under the disturbance of mine earthquake are studied and analyzed and put forward corresponding prevention and control measures. Research shows early stage of mine earthquake disturbance, roadway roof is first affected, and the principal stress of the roof has the trend of deflection to the side of the goaf. In the middle stage of mine earthquake disturbance, the main body of roof principal stress deflects to the side of goaf, and the deflection range is large. In the later stage of mine earthquake disturbance, the principal stress directions in the surrounding rock reverse rotation, and the reverse rotation angle of the principal stress direction in the roof is the largest. Finally, the asymmetric distribution characteristics of principal stress rotation are verified by using the asymmetric deformation phenomenon on both sides of roadway surrounding rock. Based on the rotation characteristics of principal stress under the dual influence of mine earthquake disturbance and goaf, optimize the layout scheme and blasting parameters of blasting pressure relief holes. The transmission direction of principal stress can be changed by blasting pressure relief method; meanwhile, the transmission of principal stress can be blocked; through the comparison of microseismic activity law before and after pressure relief, pressure relief effect is good. The research results can provide a certain reference basis for coal mine roadway pressure relief and reducing disaster conditions.

A Novel Design of Interval Type-2 Neuro-Fuzzy Controller for Flexible Structure

The aim of this research is to develop a novel design of interval type-2 neuro-fuzzy (IT2NF) controller for active vibration control of a flexible structure during an earthquake. For this purpose, two adaptive neural network based fuzzy logic controllers are designed and combined to create the novel design of an IT2NF controller to reduce the vibrations of two-storey flexible building model that occur during earthquake disturbance effects. Accordingly, dynamic modeling of a flexible structure is realized and simulated using the MATLAB / SimMechanics. Then, an experimental setup consisting of two-storey flexible structure, active mass damper (AMD) and shaker is established. Additionally, IT2NF controller is implemented in simulation and experimental models, and the effectiveness and performance of the IT2NF controller are tested under the scaled Northridge Earthquake acceleration. The obtained simulations and experimental responses are evaluated in terms of cart displacements, deflections, and accelerations of the flexible floors showing a good agreement between the simulations and the experimental results. The results show that the designed novel IT2NF controller reduced the total deflections of first and second floor by 72.3% and 68.7%, respectively, when compared with the uncontrolled system. Additionally, it is also found that the designed IT2NF controller is able to reduce the accelerations of the first and second floor by 64.8% and 54.6%, respectively. The proposed and designed control method reported in this study can be employed as an active vibration controller for multi-degree of freedom of flexible systems under the disturbances such as earthquake excitations.

Numerical Study on the Impact Instability Characteristics Induced by Mine Earthquake and the Support Scheme of Roadway

Rockburst of deep roadway was induced by the superposition of mine earthquake disturbance and high static stress exceeding the limit strength of coal‐rock mass. To study the roadway impact instability characteristics caused by mine earthquake disturbance and to propose an optimized support scheme, the discrete element model of the roadway structure was established based on the 1305 working face of the Zhaolou Coal Mine. The influence of mine earthquake amplitude and hypocenter location on the roadway was analyzed. The mesocrack evolution characteristics of the roadway were simulated and reproduced. Characteristics of stress field, crack field, displacement field, and energy field of the disturbed roadway with different support schemes were studied. The results showed that the greater the amplitude of the mine earthquake was, the severer the roadway impact failure was. The upper and left hypocenters had a significant influence on the roadway. The superposition of the high static stress and the dynamic stress due to the far‐field mine earthquake resulted in the impact instability of coal‐rock mass around the roadway, causing severe roof subsidence as well as rib and bottom heave. The evolution of tensile cracks caused the severe impact failure of roadway from a mesoscopic perspective. Using the flexible support to reinforce the roadway retarded the stress decline in roof and rib, improved the self‐stability, reduced the number of near‐field cracks, and decreased the displacement. Meanwhile, it allowed the roof and rib deformation, which was conducive to releasing elastic energy in surrounding rocks and reducing mine earthquake energy. The cracks and deformation in the floor were controlled by using the floor bolt. The optimal support scheme for a roadway to resist mine earthquake disturbance was proposed: “bolt‐cable‐mesh‐steel strip‐π‐beam + floor bolt.” The research results have a specific guiding significance for the support of the coal mine roadway.

Study on Seismic Response and Damping Measures of Surrounding Rock and Secondary Lining of Deep Tunnel

Tunnel construction is gradually developing to areas with high in situ stress; the deeper the tunnel construction, the more intense the earthquake disturbance. Under the background of frequent earthquakes, the seismic characteristics of tunnels become an important content related to the safety and stability of engineering structures. In view of the key problems of seismic response and vibration reduction measures for complex deep buried tunnels, the methods of advanced grouting and foam concrete aseismic are studied in this paper. Firstly, through geological survey, the in situ stress and geological conditions of the study area are analyzed. The structural characteristics of surrounding rock and related rock mechanics parameters are analyzed. The failure criterion of concrete lining under dynamic load is studied theoretically, and the relevant numerical calculation parameters are modified. A numerical model based on viscous boundary conditions is established. Through numerical calculation, the seismic response of tunnel surrounding rock and lining under different damping measures is analyzed. The research results have theoretical research value and social and economic benefits for ensuring the safety and stability of tunnel structure and improving the seismic fortification level.

Changes in hydrological behaviours triggered by earthquake disturbance in a mountainous watershed

Landslides induced by strong earthquakes often destroy large amounts of landscape vegetation which can trigger significant changes in runoff potential and flood flow. Little is known about hydrological behaviours imposed by co-seismic landslides and their post-earthquake evolution. Therefore, we collected time-series datasets (2007–2018) of underlying surface conditions (USC) changes including landslide expansion and recovery in a watershed affected by the Wenchuan earthquake to further quantify how the large physical disturbance affected the flood hydrological behaviours. The hydrological model HEC-HMS was calibrated and validated to predict the historical hydrological behaviours based on 5 min time-series data in rainfalls and streamflow (2018–2019), showing a good model performance with a mean Nash–Sutcliffe efficiency of 0.76. It was found that, shortly after the earthquake, the sharp expansion with 11% of landslide areas elevated the magnitudes of runoff potential, peak discharge, and runoff volume by >10%, and the peak to time for the high-magnitude flood was advanced by 25 min compared to the pre-earthquake levels. The tipping point along the hydrological disturbance–recovery trajectory was detected within 2011 with higher flood peaks and volumes, and the periods of 2011–2013 (i.e. 3–5 years post-earthquake) were deemed to be a rapid recovery period, revealing an unstable hydrological function. These findings are significant for clearly understanding the magnitude and timing, as well as greater risks of post-earthquake catastrophic flooding in earthquake-stricken regions. Additionally, the post-earthquake accompanied rainstorm-induced geohazards, which limited the recovery of landscape vegetation, triggering an undulant but clear recovery process (1–7 years post-earthquake) of hydrological behaviours. These findings promoted our understanding of the spatiotemporal evolution of hydrological behaviours triggered by the earthquake, and further contribute to the development of adaptation and mitigation strategies for the unpredictable flash floods triggered by future abrupt natural hazards in earthquake-affected regions.

Structural seismic resilience evaluation through real-time hybrid simulation with online learning neural networks

Seismic resilience provides a comprehensive assessment of the ability of a community to withstand and recover from earthquake disturbances. To support the design of seismic resilient structures, quantitative assessment of seismic resilience is needed and requires numerical simulations to be performed under a risk-based context. The associated large uncertainties can lead to large computational costs and limited accuracy in the numerical simulation, especially for structural systems with critical components having complex nonlinearity and rate-dependent behaviour. To cope with such uncertainties and address simulation accuracy, a framework integrating real-time hybrid simulation is proposed to ensure the assessment accuracy of the seismic resilience of structures. With real-time hybrid simulation, modelling accuracy under wide range of design scenarios can be improved. To more efficiently develop fragility curves using the results of real-time hybrid simulation, experimental substructure component metamodelling is included through an online learning approach using long-short-term memory neural networks. The proposed integration of real-time hybrid simulation and metamodelling in the fragility analysis to support resilience assessment is demonstrated through a proof-of-concept case study on the seismic retrofit of a six-storey building using inter-storey isolation.

Macroalgal Bioindicators of Recovery from Eutrophication in a Tidal Lagoon Following Wastewater Diversion and Earthquake Disturbance

Together, macroalgal tissue biochemical nitrogen indices (N-indices) and macroalgal abundance can be used as bioindicators of N-enrichment in estuaries. In this study, we examine the extent and rates of response of Ulva bioindicators during rapid N-enrichment perturbations in the eutrophic Avon-Heathcote Estuary (AHE) (Christchurch, New Zealand). With the diversion of the city’s wastewater discharge away from the estuary in March 2010, a ~ 90% reduction in the estuary’s N-concentration was expected. In turn, this was expected to reduce macroalgal biomass and improve the overall trophic condition of the estuary. We surveyed Ulva bioindicators over a five-year period spanning the diversion. There was a rapid (within one year) transition away from eutrophic condition reflected in N-indices (tissue-chlorophyll, -free amino acids, -N and -δ15N) following wastewater diversion, towards values corresponding with ‘cleaner’ water quality. This was accompanied by large reductions in Ulva percent cover, based on seasonal surveys conducted from 2001 to 2014. However, two large earthquakes in February and June 2011 caused a breakdown of the city’s wastewater infrastructure, resulting in overflows of untreated sewage into the estuary between February and November 2011. The re-enrichment of N and changes in N-sources (treated versus untreated sewage) were rapidly reflected in Ulva bioindicators, notably δ15N. Following repair of infrastructure, Ulva bioindicators again reverted towards a less eutrophic state. Overall, bioindicators were sensitive to changes in N-availability and N-source, and useful for identifying the position of algal populations on a eutrophic-to-oligotrophic gradient. These attributes demonstrated their utility as adjuncts to water quality monitoring and algal biomass surveys.

Temporal and Spatial Evolution of Vegetation Coverage in the Mianyuan River Basin Influenced by Strong Earthquake Disturbance

The 2008 Wenchuan earthquake caused significant economic losses and degradation of regional ecosystems, including the terrestrial vegetation. Since the vegetation root system can enhance the soil’s anti-erosion capacity and therefore mitigate the occurrence of slope instabilities, it is beneficial to study the spatial and temporal evolution of vegetation for a long-term assessment of co-seismic secondary disasters. The Mianyuan River Basin, an uninhabited area passing through an active fault located in the earthquake-affected region, was selected as the study area. The Normal Difference Vegetation Index (NDVI) was calculated using remote sensing images from 1994 to 2017 to analyze the process of vegetation growth, loss, fluctuation and recovery. Statistical results suggest that the area in the middle and lower reaches, near the river network, and with a slope of 30 to 40 degrees were variable regions, showing more significant vegetation destruction during the earthquake and faster repair after the seismic event. Besides, vegetation near the fault was damaged more severely after the earthquake, but the active fault did not play an essential role in the vegetation recovery period. In the Mianyuan River Basin, vegetation experienced a volatility period (5 plus or minus one year) before entering the recovery period. In 8 to 9 years after the earthquake, the surficial vegetation could recover to the state before the earthquake.