Coastal Subsidence Research Articles

Assessing Current Coastal Subsidence at Continental Scale: Insights From Europe Using the European Ground Motion Service

AbstractBeside climate‐change‐induced sea‐level rise (SLR), land subsidence can strongly amplify coastal risk in flood‐prone areas. Mapping and quantifying contemporary vertical land motion (VLM) at continental scales has long been a challenge due to the absence of gridded observational products covering these large domains. Here, we fill this gap by using the new European Ground Motion Service (EGMS) to assess the current state of coastal VLM in Europe. First, we compare the InSAR‐based EGMS Ortho (Level 3) with nearby global navigation satellite systems (GNSS) vertical velocity estimates and show that the geodetic reference frame used to calibrate EGMS strongly influences coastal vertical land velocity estimates at the millimeter per year level and this needs to be considered with caution. After adjusting the EGMS vertical velocity estimates to a more updated and accurate International Terrestrial Reference Frame (ITRF2014), we performed an assessment of VLM in European low elevation coastal flood plains (CFPs). We find that nearly half of the European CFP area is, on average, subsiding at a rate faster than 1 mm/yr. More importantly, we find that urban areas and populations located in the CFP experience a near −1 mm/yr VLM on average (excluding the uplifting Fennoscandia region). For harbors, the average VLM is even larger and increases to −1.5 mm/yr on average. This demonstrates the widespread importance of continental‐scale assessments based on InSAR and GNSS to better identify areas at higher risk from relative SLR due to coastal subsidence.

Understanding land subsidence in the Pearl River Delta region of China based on InSAR observations

Land subsidence occurs in river delta areas. A comprehensive understanding of the factors contributing to land subsidence is crucial for effective geohazard mitigation and land planning. This study investigates the distribution characteristics and spatiotemporal evolution pattern of the land subsidence in the Pearl River Delta based on the InSAR-derived ground deformation data spanning 2016 to 2021; and, the effects of the influencing factors, including the Quaternary sediment thickness, land use classification, land reclamation, and subway construction and operation, on the subsidence are analyzed. The results unveil the presence of four major subsidence zones and several minor coastal subsidence bowls in the research area, with a total area of about 1100 km, all of which exhibit prolonged and intense subsidence. In the remaining regions, land subsidence predominantly exhibits weak and short-term occurrences. The subsidence in the study area follows a distinct linear evolutionary pattern with a slight rebound, potentially linked to the rise of groundwater levels. Regions with Quaternary sediment thickness surpassing 20 m, engaging in aquaculture or agricultural activities, and featuring reclaimed land are predisposed to prolonged and intense ground subsidence. In addition, the construction and operation of subway lines may induce ground subsidence, especially in geologically vulnerable areas. This study provides valuable insights into land subsidence research in delta regions.

Mangrove vegetation response to alteration in coastal geomorphology after an earthquake in Andaman Islands, India

The 2004 Sumatra-Andaman earthquake caused a devastating tsunami and shifts in land elevations, which had an instantaneous as well as the long-term impact on the Andaman Islands. Especially, the coastal uplift and subsidence has altered the tidal regime, leading to mass mortality and degradation of mangroves (∼150 sq. km). The tectonic shift in the Andaman archipelago has created three broader geographical units: North Andaman with coastal uplift (∼1.3 m) – sea level drop (SLD) scenario; Middle Andaman with minor to no change in coastal geomorphology – no change scenario; and South Andaman with coastal subsidence (∼1.1 m) – sea level rise (SLR) scenario. How these changes in the tidal regime have influenced mangrove vegetation remains less understood. Therefore, we assessed mangrove vegetation characteristics across the Andaman Islands to examine mangrove response to coastal uplift and subsidence after 18 years since the disturbance. The uplifted sites mimicking the SLD scenario appeared more destructive to mangroves (tree density - 771/ha) in comparison to subsided sites mimicking the SLR scenario (tree density - 937/ha), while no change sites with the highest tree density (1288/ha) showed lowest impacts to mangrove. The species diversity (H’=Shannon-Wiener index) within recruitment cohorts (seedlings: <1 cm DBH and saplings: ≥1 cm and <5 cm DBH) sapling (H’=1.57), and seedling (H’=1.48) was significantly higher than the trees (H’=1.20). Rhizophora apiculata and Ceriops tagal were the dominant species (cumulative IVI 60%) found in survived mangrove forests demonstrating their high resilience for sudden changes in tidal regime. Our study provided a comprehensive account of mangrove vegetation response after a major disruptive event in 2004. Long-term monitoring of these novel sites would enhance our understanding of mangrove response to sea level change, which can also provide significant insights for the restoration and management of mangroves.

Viscoelastic earthquake cycle model for the Caribbean subduction zone in northwestern Colombia: Implications of coastal subsidence for seismic/tsunami hazards

Recent interplate coupling results from the inversion of GPS data in northwestern Colombia have shed light on the seismogenic and tsunami potential along the Caribbean coast. The identified locked region on the subduction interface could generate an Mw8.0 earthquake every 600 years, followed by a tsunami. While observed horizontal velocities have been reproduced successfully by the elastic coupling model, vertical velocities remain unexplained and differ, both in their signs and magnitudes, from the model prediction. To explain 3-dimensional velocities, particularly rapid coastal subsidence, we evaluate the viscoelastic response of the lithosphere-asthenosphere system to an earthquake cycle at the Caribbean subduction zone. We confirm that the role of viscous relaxation on interseismic deformation is critical when the recurrence interval is longer than the asthenosphere relaxation time. Moreover, fitting observed crustal motions requires a strong lithosphere (60–100 km) consistent with the depth of the lithosphere-asthenosphere boundary. Our results support the hypothesis of the Caribbean as a locus of seismic and tsunami hazards but do not resolve the vertical motion paradox at different time scales since the interseismic crustal motions recover completely the coseismic and postseismic displacements caused by the potential mainshock. Supplementary geological investigation is essential to validate our current interpretation and resolve the remaining gaps.

Characteristics and Geological Conditions of Coastal Zone Quaternary Sediment Formations in The Binh -Tri -Thien Area under The Context of Global Sea Level Change

Quaternary sediments in the Binh Tri Thien coastal zone are diverse in both material composition and development history. From land to sea, there are 4 structural regions: i) marginal plain region; ii) Coastal lagoon region; iii) Coastal sand dunes region; and iv) Monocline coastal subsidence region. In the vertical direction, all four regions have five sedimentary cycles as follows: a) Early Pleistocene (Q11); b) Early middle Pleistocene (Q12a); c) Late middle Pleistocene (Q12b); d) Early late Pleistocene (Q13a); e) Late late Pleistocene (Q13b-Q2). Four structural zones are characterized by different lithofacies complexes: 1) In the lowstand systems tract (LST) at the beginning of each cycle in all 4 structural zones, the SmaLST facies complex is present; 2) In the transgressive systems tract (TST), there are the following lithofacies complexes: a) region I: MsbTST; b) region II: MlgTST; c) region III: SmTST; d) region IV: Msam,mTST; 3) In the highstand systems tract (HST) there are the following facies complexes: a) Region I: (MsabHST); b) Region II: MslgHST; c) Region III: SmvHST; d) Region IV: SmmHST. The difference in sedimentary facies in the transgressive and highstand systems tract depends on the differentiation of four geological structure regions.&#x0D;

Disappearing cities on US coasts

The sea level along the US coastlines is projected to rise by 0.25–0.3 m by 2050, increasing the probability of more destructive flooding and inundation in major cities1–3. However, these impacts may be exacerbated by coastal subsidence—the sinking of coastal land areas4—a factor that is often underrepresented in coastal-management policies and long-term urban planning2,5. In this study, we combine high-resolution vertical land motion (that is, raising or lowering of land) and elevation datasets with projections of sea-level rise to quantify the potential inundated areas in 32 major US coastal cities. Here we show that, even when considering the current coastal-defence structures, further land area of between 1,006 and 1,389 km2 is threatened by relative sea-level rise by 2050, posing a threat to a population of 55,000–273,000 people and 31,000–171,000 properties. Our analysis shows that not accounting for spatially variable land subsidence within the cities may lead to inaccurate projections of expected exposure. These potential consequences show the scale of the adaptation challenge, which is not appreciated in most US coastal cities.

InSAR and machine learning reveal new understanding of coastal subsidence risk in the Yellow River Delta, China

Coastal subsidence is a geological disaster that has devastating consequences. However, an accurate understanding of its risks involves more than simply assessing the amount or rate of land subsidence. The existing methods used to evaluate geological disaster risks depend on extensive data collection, entail substantial workloads, suffer from error estimation challenges, and lack regional adaptability. These limitations prevent us from fully understanding coastal subsidence risks in estuarine deltas. Therefore, in this study, we propose a new subsidence risk assessment method that addresses the challenges of traditional geological risk assessments in terms of spatial coverage, spatiotemporal resolution, and data collection difficulty. First, Sentinel-1 multitemporal interferometric synthetic aperture radar (MT-InSAR) and cluster analysis were used to estimate the subsidence hazards. Subsequently, Landsat-8 imagery and a random forest (RF) classifier were used to obtain land use and land cover (LULC), and the analytic hierarchy process (AHP) was used to obtain settlement vulnerability. Thereafter, subsidence susceptibility was derived from the sediment layer thickness. By combining subsidence hazard, vulnerability, and susceptibility, the first subsidence risk map with a 30 m resolution was generated. The results showed that 4.54 % of the Yellow River Delta (YRD) area was high-risk, 8.75 % was medium-risk, and 10.14 % was low-risk. Notably, the risk map shows a clear overlap between high-risk and saltwater mining areas in the YRD. The proposed method is expected to improve our understanding of the coastal subsidence risk in estuarine deltas. Considering that the risk in high-value economic areas in the YRD is increasing, whereas the risk in low-value economic areas may change owing to human activity, early preventive measures are required.

Integrated Assessment of Coastal Subsidence in Nansha District, Guangzhou City, China: Insights from SBAS-InSAR Monitoring and Risk Evaluation

Monitoring and assessing coastal subsidence is crucial to mitigating potential disaster risks associated with rising sea levels. Nansha District in Guangzhou City, representing global coastal soft-soil urban areas, faces significant challenges related to ground subsidence. However, the current understanding of the status, causative factors, and risk (includes subsidence susceptibility and vulnerability) assessment of ground subsidence in Nansha District is unclear. To address this gap, we utilized the SBAS-InSAR technique, analyzing 49 Sentinel-1A images from December 2015 to June 2019, for systematic ground subsidence monitoring. Subsequently, we assessed subsidence risk using a comprehensive index method and a risk matrix. Our findings indicate that subsidence velocity primarily ranged from −40 to −5 mm/a, with a spatial pattern of increasing subsidence from inland to coastal areas. The cumulative subsidence process unfolded in four distinct stages. The genesis of land subsidence was linked to an endogenous geological context dominated by soft-soil deposition, influenced by external factors such as surface loading and groundwater extraction. High-risk zones were concentrated in key engineering development areas, transportation pipeline trunk lines, and densely populated regions, demanding special attention. This study provides a foundational resource for disaster prevention and control strategies in Nansha District and similar coastal cities.

What is coastal subsidence?

Abstract Major technological advances have made measurements of coastal subsidence more sophisticated, but these advances have not always been matched by a thorough examination of what is actually being measured. Here we draw attention to the widespread confusion about key concepts in the coastal subsidence literature, much of which revolves around the interplay between sediment accretion, vertical land motion and surface-elevation change. We attempt to reconcile this by drawing on well-established concepts from the tectonics community. A consensus on these issues by means of a common language can help bridge the gap between disparate disciplines (ranging from geophysics to ecology) that are critical in the quest for meaningful projections of future relative sea-level rise.

A 5000 yr record of coastal uplift and subsidence reveals multiple source faults for past earthquakes on the central Hikurangi margin, New Zealand

Abstract Prehistoric records of subduction earthquakes are often distinguished by evidence of synchronous widespread coastal deformation, the extent of which negates the plausibility of alternative source faults. At the Hikurangi subduction margin in New Zealand, untangling the record of subduction interface ruptures is complicated. Large earthquake age uncertainties inhibit unique solutions of along-strike correlations, and complex patterns of coastal deformation caused by upper-plate faulting prevent reliable indication of source faults. In this work, we improved paleoearthquake reconstructions on the central Hikurangi margin with a new, well-constrained 5000 yr earthquake record from Pakuratahi Valley near Napier, North Island, New Zealand. Evidence of laterally extensive paleoenvironmental changes is consistent with coseismic subsidence and coseismic uplift in large earthquakes. Radiocarbon dates on fragile terrestrial macrofossils and tephra isochrons were used to construct robust age models that yielded earthquake ages of 4839–4601 calibrated (cal.) yr B.P., 3630–3564 cal. yr B.P., 2687–2439 cal. yr B.P., and 1228–823 cal. yr B.P. Integration of these ages with refined earthquake chronology from nearby Ahuriri Lagoon indicated that the next large earthquake impacting the Napier area is more likely to cause coastal subsidence than uplift. Drawing on correlations with cotemporal evidence elsewhere on the central margin, we infer that the overall patterns of coseismic deformation could be generated by either rupture of the subduction interface or upper-plate faults, or both. This inability to separate source faults for past earthquakes limits the efficiency of forecasting future earthquakes. Similar problems of intertwined paleoearthquake signatures likely apply to other plate boundaries, where we recommend cautious interpretation of coastal deformation to accurately address the hazard from both types of source faults.

Sentinel-1 InSAR-derived land subsidence assessment along the Texas Gulf Coast

Mapping large-scale coastal subsidence is significant in providing valuable support to decision-making stakeholders to recognize impacts of potential natural disasters. However, this task presents significant challenges due to its highly complex nature of the spatial–temporal variability. Recent advances in the observation capability of synthetic aperture radar (SAR) missions and the processing algorithms of interferometric SAR (InSAR) techniques have made it possible to efficiently map large-scale subsidence from space. This study utilized the persistent scatterer (PS) InSAR method to process four swathes of Sentinel-1 SAR images captured between 2016 and 2022 to map large-scale subsidence along the Texas coastline. The subsidence map, encompassing over 1.7 million PS points, was calibrated/validated with observations of 115 continuously operating global navigation satellite system (cGNSS) stations. Nineteen subsiding hotspots were identified and potential subsidence drivers were analyzed, including hydrocarbon extraction (HE), groundwater withdrawal (GW), and salt domes. The results suggest that HE activities were the primary driver of observed subsidence in the Coastal Bend and South Texas, as well as in the Southeast Texas regions. In the Houston-Galveston Area, subsidence appears to be influenced by a combination of GW, HE, and salt dome movements. Within 50 km of the Texas shorelines, subsidence rates were approximately −1.0 mm/yr within the coastal vicinity, while inland areas experience a gradually increasing trend. Specific coastal areas, such as Corpus Christi, Freeport, Seabrook, San Leon, and others, may face elevated flooding risks during high tide and storm events with the sea-level rise trend up to 24.0 mm/yr in relation to coastal subsiding land.

Three decades of coastal subsidence in the slow-moving Nice Côte d'Azur Airport area (France) revealed by InSAR (interferometric synthetic-aperture radar): insights into the deformation mechanism

Abstract. Coastal areas can be tremendously biodiverse and host a substantial part of the world's population and critical infrastructure. However, there are often fragile environments that face various hazards such as flooding, coastal erosion, land salinization or pollution, earthquake-induced land motion, or anthropogenic processes. In this article, we investigate the stability of the Nice Côte d'Azur Airport, which has been built on reclaimed land in the Var River delta (French Riviera, France). This infrastructure, as well as the ongoing subsidence of the airport runways, has been a permanent concern since the partial collapse of the platform in 1979. Here, we used the full archive of ESA SAR (synthetic-aperture radar) images from 1992 to 2020 to comprehensively monitor the dynamics of the airport subsidence. We found that the maximum downward motion rate has been slowing down from 16 mm yr−1 in the 1990s to 8 mm yr−1 today. However, sediment compaction is still active, and an acceleration phase of the continuous creep leading to a potential failure of a part of the platform cannot be excluded. Our study demonstrates the importance of remotely monitoring of the platform to better understand the motion of coastal land, which will ultimately help evaluate and reduce associated hazards.

Impact of Hypocenter Location on Rupture Extent and Ground Motion: A Case Study of Southern Cascadia

AbstractThe Cascadia subduction zone has well‐documented geological records of megathrust earthquakes with the latest ∼Mw 9 rupture occurring in CE 1700. The paleoseismic observations suggest that southern Cascadia is mature for future earthquakes since the last event. Consequently, it is crucial to investigate the potential rupture scenarios. Although existing interseismic locking models share similar moment deficits, whether future earthquakes would be margin‐wide or segmented, as suggested by paleoseismic records, remains unknown. Accordingly, we aim to investigate: (a) possible rupture segmentation patterns, (b) whether south Cascadia can host margin‐wide ruptures, and (c) whether the existing locking models suggest similar future rupture scenarios. Assuming constant effective normal stress, we estimate the stress distribution constrained by the locking models (i.e., Gamma model from Schmalzle et al. (2014, https://doi.org/10.1002/2013GC005172), the preferred model from S. Li et al. (2018, https://doi.org/10.1029/2018JB015620), and the best‐fit model from Lindsey et al. (2021, https://doi.org/10.1038/s41561-021-00736-x)) from static calculation and discover they lead to different stress distributions, indicating distinct seismic potentials. Our dynamic rupture scenarios show that the south can generate both segmented ruptures (&gt;Mw 7.3–8.4) and margin‐wide ruptures (&gt;Mw 8.6) depending on the hypocenter location. The along‐strike rupture length appears to coincide with rupture lengths hypothesized from paleoseismology, and the Schmalzle model produces reasonable coastal subsidence amplitudes from the CE 1700 event. Therefore, we propose that three high‐slip trench‐breaching patches are sufficient for reproducing historical subsidence records. Our results can be further applied in seismic and tsunami hazard assessment, and serve as a comparison for non‐trench‐breaching scenarios.

The 95 per cent confidence interval for the mean sea-level change rate derived from tide gauge data

SUMMARYTide gauge (TG) data are crucial for assessing global sea-level and climate changes, coastal subsidence and inundation. Mean sea-level (MSL) time-series derived from TG data are autocorrelated. The conventional ordinary least-squares regression method provides reasonable estimates of relative sea-level (RSL) change rates (linear trends) but underestimates their uncertainties. In order to cope with the autocorrelation issue, we propose an approach that uses an ‘effective sample size’ (${N}_{\mathrm{ eff}}$) to estimate the uncertainties (±95 per cent confidence interval, or 95 per cent CI for short). The method involves decomposing the monthly MSL time-series into three components: a linear trend, a periodic component and a noise time-series. The ${N}_{\mathrm{ eff}}$ is calculated according to the autocorrelation function (ACF) of the noise time-series. We present an empirical model that fits an inverse power-law relationship between 95 per cent CI and time span (T) based on 1160 TG data sets globally distributed, where $95\ \mathrm{ per}\ \mathrm{ cent}\,\mathrm{ CI} = 179.8{T}^{ - 1.29}$. This model provides a valuable tool for projecting the optimal observational time span needed for the desired uncertainty in sea-level rise rate or coastal subsidence rate from TG data. It suggests that a 20-yr TG time-series may result in a 3–5 mm yr−1 uncertainty (95 per cent CI) for the RSL change rate, while a 30-yr data set may achieve about 2 mm yr−1 uncertainty. To achieve a submillimetre per year (&amp;lt; 1 mm yr−1) uncertainty, approximately 60 yr of TG observations are needed. We also present a Python module (TG_Rate_95CI.py) for implementing the methodology. The Python module and the empirical model have broad applications in global sea-level rise and climate change studies, and coastal environmental and infrastructure planning, as well as Earth science education.

Stratigraphic evidence of relative sea level changes produced by megathrust earthquakes in the Jalisco subduction zone, Mexico. The signature of the 1995 Colima-Jalisco earthquake (Mw 8) as a modern analogue

Geological evidence of megathrust earthquakes along the Mexican Pacific coast relies predominantly on tsunami deposits. Records of coseismic relative sea-level changes are scarce even though such evidence can complement and constrain tsunami records, providing information to reconstruct past earthquake rupture dimensions to improve the earthquake hazard assessment of the region. This paper provides the first diatom-based quantitative reconstruction of coastal subsidence along the Mexican subduction zone through the analysis of coastal wetland sediments. We use the stratigraphic signature of the 1995 Colima-Jalisco earthquake (Mw 8.0) as this earthquake is instrumentally well-constrained, allowing us to evaluate our findings and establish approaches to investigate earlier earthquakes. Deposits beneath the wetland Estero Potrero Grande reveal a stratigraphic sequence, < 28 cm beneath the wetland surface, that resembles a signature of rapid submergence. This sequence consists of a horizontal bed of silt with highly humified organic matter abruptly overlain by a horizontal bed of grey silt. The abrupt stratigraphic contact between the two units extends across >1 km of the wetland. Using 14C ages and 137Cs chronohorizons to build an age-depth model, we estimate the age range (1985–2003 CE) and mean age (1995 CE) of this abrupt stratigraphic contact, coincident with the year of the earthquake. Three elemental log-ratios (S/Zn, Br/Zn and Ca/Zn) indicate an abrupt increase of salinity across the stratigraphic contact, which we interpret as marsh submergence recording coseismic coastal subsidence, reflected as relative sea-level rise. Fossil diatom assemblages confirm this trend, and through quantitative approaches we estimate its magnitude (−0.06 ± 0.08 m and − 0.11 ± 0.23 m), which is comparable with coastal subsidence measured by geodetic instruments. Our records reveal a millimetric spike of sand, which we interpret as a signature of the tsunami that accompanied this great earthquake. These findings demonstrate that coastal wetland sediments from the Mexican Pacific coast can record tectonic induced relative sea-level changes. This approach can allow us to better understand the long-term spatial and temporal behavior of this subduction zone.

Wintertime Synoptic Patterns of Midlatitude Boundary Layer Clouds Over the Western North Atlantic: Climatology and Insights From In Situ ACTIVATE Observations

AbstractThe winter synoptic evolution of the western North Atlantic and its influence on the atmospheric boundary layer is described by means of a regime classification based on Self‐Organizing Maps applied to 12 years of data (2009–2020). The regimes are classified into categories according to daily 600‐hPa geopotential height: dominant ridge, trough to ridge eastward transition (trough‐ridge), dominant trough, and ridge to trough eastward transition (ridge–trough). A fifth synoptic regime resembles the winter climatological mean. Coherent changes in sea‐level pressure and large‐scale winds are in concert with the synoptic regimes: (a) the ridge regime is associated with a well‐developed anticyclone; (b) the trough‐ridge gives rise to a low‐pressure center over the ocean, ascents, and northerly winds over the coastal zone; (c) trough is associated with the eastward displacement of a cyclone, coastal subsidence, and northerly winds, all representative characteristics of cold‐air outbreaks; and (d) the ridge–trough regime features the development of an anticyclone and weak coastal winds. Low clouds are characteristic of the trough regime, with both trough and trough–ridge featuring synoptic maxima in cloud droplet number concentration (Nd). The Nd increase is primarily observed near the coast, concomitant with strong surface heat fluxes exceeding by more than 400 W m−2 compared to fluxes further east. Five consecutive days of aircraft observations collected during the ACTIVATE campaign corroborates the climatological characterization, confirming the occurrence of high Nd for days identified as trough. This study emphasizes the role of boundary‐layer dynamics and aerosol activation and their roles in modulating cloud microphysics.

Hidden vulnerability of US Atlantic coast to sea-level rise due to vertical land motion

The vulnerability of coastal environments to sea-level rise varies spatially, particularly due to local land subsidence. However, high-resolution observations and models of coastal subsidence are scarce, hindering an accurate vulnerability assessment. We use satellite data from 2007 to 2020 to create high-resolution map of subsidence rate at mm-level accuracy for different land covers along the ~3,500 km long US Atlantic coast. Here, we show that subsidence rate exceeding 3 mm per year affects most coastal areas, including wetlands, forests, agricultural areas, and developed regions. Coastal marshes represent the dominant land cover type along the US Atlantic coast and are particularly vulnerable to subsidence. We estimate that 58 to 100% of coastal marshes are losing elevation relative to sea level and show that previous studies substantially underestimate marsh vulnerability by not fully accounting for subsidence.

Application of Stress Parameter from Liquefaction Analysis on the Landslide Induced Tsunami Simulation: A Case Study of the 2018 Palu Tsunami

The accuracy of numerical simulations of a landslide-induced tsunami depends on the landslide characteristics, such as landslide geometry and geotechnical parameters. However, owing to the difficulty in sampling and measuring submarine landslides, rough assumptions of landslide parameters typically lead to significant uncertainties. In the 2018 Palu event, the earthquake was followed by immediate cascading disasters of coastal subsidence, both land and submarine landslides and a tsunami. This scenario provides opportunities to analyze landslide phenomena on land to characterize the submarine landslide causing the tsunami. This study proposes a new approach of using shear-stress parameters obtained from liquefaction analyses as input for landslide-induced tsunami simulation. To obtain the submarine landslide parameter, using the finite element method we modeled the liquefaction happened in Jono-Oge located near Palu Valley area. The shear-stress in this area was quite small with the range 1.5–3.5 kPa. We found that tsunami simulation yielded better accuracy by applying the stress value range obtained from the liquefaction analysis on land (1.5 kPa) rather than the typically adopted stress value for general cases (20 kPa). The result from the tsunami simulation using two-layer method with identical landslide location and geometry showed that shear-stress value of landslide mass gave quite a significant effect to the tsunami height.

Toward sustainable inland aquaculture: Coastal subsidence monitoring in Taiwan

Inland aquaculture is a major industry that provides fish to reduce the stress of oceans in supplying global protein consumption. Developed and developing nations house their inland aquaculture industries largely in coastal areas, where groundwater is pumped to supply the needed water in a non-sustainable way that leads to coastal land subsidence. This study shows a comprehensive picture of land subsidence in Pingtung, a coastal plain in southern Taiwan, where, after the gradual abandonment of rice cultivation, huge groundwater exploitation has occurred since the 1970s to feed inland aquaculture. Integrated interpretation of multidevice monitoring results has improved knowledge of land subsidence associated with land uses and groundwater pumping. Results indicate a maximum cumulative subsidence of 350 cm from 1972 to 2019 near the aquaculture-rich township of Linbian. Sub-surface displacement measurements using multilayer compaction wells identified the de-watered layers responsible for the land subsidence in four sinking-affected coastal areas, where different groundwater usage patterns lead to different patterns of aquifer-system compactions at varying depths. The use of SAR interferometry with high spatial resolution and frequent revisit times has made it possible to overcome the inherent limitations of ground-based measurement methodologies such as leveling, continuous global navigation satellite system, and multilayer compaction wells, which while very accurate do not allow for adequate monitoring of subsidence in the Pingtung coastland due to the high dynamics and spatial variability of the process. Based on the results of this study, several sustainable aquaculture-related actions are being implemented or have been proposed to reduce the risks of land subsidence, flooding, and salinization in Pingtung. These include the use of InSAR monitoring for conventional sensors to continuously and timely monitor land subsidence.

Salinification of Coastal Wetlands and Freshwater Management to Support Resilience

Climates are rapidly changing in wetland ecosystems around the world and historical land-use change is not always given enough consideration in climate adaptation discussions. Historical changes to hydrology and other key environments can exacerbate vegetation stress; e.g., recent drought and flood episodes are likely more extreme because of climate change. The contributions of global and regional changes that affect groundwater and surface water availability all need consideration in conservation planning including sea-level rise, coastal subsidence and compaction, fluid extraction, and floodplain reengineering. Where subsidence is not too extreme, healthy coastal vegetation often can keep ahead of sea-level rise by accreting elevation through sedimentary and/or biogenic processes. Better water conservation and minimum water delivery during drought may support foundational species and avoid wetland collapse. Local approaches have been developed to rewet inland floodplains decades after their reengineering for agricultural and urban development to support biodiversity in salinified coastal wetlands. The purpose of this paper is to describe inland wetland remediation techniques that may also be useful to increase freshwater delivery to coastal wetlands experiencing salinification. While some salinified coastal ecosystems may transition in the future, attempts can be made to remediate salinification related to historical land use in support of wetland conservation, health, and sustainability.