A method for researching maximum credible earthquake of dam site in high altitude and high seismic region

Abstract

The application belongs to the field of dam stability evaluation, and provides a research method for maximum credible earthquake of dam site in high-altitude and high-seismicity area, S1: obtaining geological, seismic, topography and environmental characteristic data of dam site in high-altitude and high-seismicity area, and historical seismic activity and focal parameter data, and preprocessing and standardizing the data; S2: constructing a high-altitude seismic wave propagation and attenuation coupling model; S3: identifying and quantifying main seismogenic structures and potential focal parameters in the region, and constructing a probability model for potential focal sources in the region; S4: dividing the focal source region and defining characteristic focal events, constructing a single-focal-source and multi-focal-source superposition simulation scenario, determining the required seismic ground motion records and physical parameters for simulation, and formulating the regional grid and boundary conditions for simulation calculation; S5: performing fine simulation calculation of seismic ground motion parameters at the dam site based on the coupling model, and extracting and calculating the seismic ground motion parameters at the dam site.

Description

Technical Field

[0001] This invention belongs to the field of dam stability assessment and relates to a method for studying the maximum credible earthquake at dam sites in high-altitude, high-seismic-zone areas. Background Technology

[0002] In recent years, a series of high-altitude, high-seismic-zone dams have been planned, under construction, or completed in earthquake-prone areas. Their seismic performance may exhibit fundamental differences, ranging from quantitative to qualitative, compared to dams with heights of 100 meters. Furthermore, the inherent complexity of arch dam structures and the continuously increasing seismic fortification intensity at dam sites in strong earthquake zones have made the seismic safety of high arch dams increasingly prominent. Simultaneously, research on the maximum credible earthquake in the dam site area has become a crucial issue for ensuring project safety. Existing research methods largely focus on the analysis of regional tectonics and seismic geology data, and assess seismic motion parameters by simulating the effects of different or all earthquake sources. However, these methods still have certain limitations in terms of applicability, accuracy, and comprehensiveness under specific environments, making it difficult to fully meet the needs of refined research on complex seismic effects at dam sites in high-altitude, high-seismic-zone areas.

[0003] Chinese Patent Publication No. CN109375252A discloses a method for evaluating seismic motion parameters considering the maximum credible earthquakes from different seismogenic structures. This patent designs a seismic motion simulation scheme considering the influence of different seismic sources based on regional tectonic and seismic geological data, and employs the stochastic finite fault method to simulate seismic motion at the site, ultimately comprehensively evaluating the site's seismic motion parameters. However, this technical solution relies solely on the calculation results or envelope of a single seismic source as site parameters, neglecting the complex influence of unique topography, climate conditions, and the superposition effects of multiple seismic sources on seismic motion propagation in high-altitude, high-seismic-region areas. This may lead to discrepancies between the parameter evaluation results and actual seismic action. Furthermore, this method does not fully consider the impact of the special environment of high-altitude areas on the attenuation law of seismic wave propagation, potentially reducing its applicability in dam site research in high-altitude, high-seismic-region areas.

[0004] The above problems indicate that existing maximum credible earthquake research methods still have certain shortcomings in their application to dam sites in high-altitude, high-seismic-zone areas, in terms of comprehensively considering topographic and environmental factors, refining the analysis of the superposition effects of multiple seismic sources, and improving the accuracy of seismic motion parameter evaluation. Summary of the Invention

[0005] To address the problems in existing technologies, this invention provides a method for studying the maximum credible earthquake at dam sites in high-altitude, high-seismic-zone areas. The method aims to optimize the seismic motion parameter evaluation model by combining the unique environmental conditions of high altitudes, thereby improving the accuracy and applicability of the research results and providing more reliable support for the safe design of dam projects in high-altitude, high-seismic-zone areas.

[0006] The present invention adopts the following technical solution, including the following steps: S1: Obtain geological, seismic, topographic and environmental characteristics data of the dam site area in high-altitude and high-seismic-risk areas, as well as historical seismic activity and source parameter data, and preprocess and standardize the data. S2: Construct a coupled model for the propagation and attenuation of high-altitude seismic waves; S3: Identify and quantify the main seismogenic structures and potential seismic source parameters in the region, including identifying potential seismogenic faults based on geological structural data, determining the geometric parameters and activity characteristics of fault zones, and constructing probabilistic models for potential seismic sources in the region. S4: Divide the source region and define characteristic source events, construct simulation scenarios of single-source and multi-source superposition, determine the ground motion records and physical parameters required for simulation, and formulate the regional grid and boundary conditions for simulation calculation; S5: Based on the coupling model, perform refined simulation calculations of the ground motion parameters at the dam site, including embedding the high-altitude seismic wave propagation and coupling attenuation function into the ground motion simulation software, applying a multi-source combined ground motion scenario, dynamically adjusting the attenuation characteristics of the seismic waves during the propagation process, and extracting and calculating the ground motion parameters at the dam site; and comprehensively evaluating the maximum credible ground motion parameters at the dam site and performing uncertainty analysis.

[0007] Preferably, the acquisition of geological, seismic, topographic, and environmental characteristics data of the dam site area in high-altitude, high-seismic-zone areas includes: collecting regional geological structure and rock and soil properties data. The collection includes identifying the distribution of active faults through remote sensing image analysis, aerial photogrammetry, and on-site geological surveys; combining geophysical exploration to detect the sequence structure, lithological distribution, geological interface depth, and hidden faults of underground rock and soil; and obtaining basic physical and mechanical parameters and nonlinear dynamic characteristics of rocks or soils through borehole sampling and indoor and outdoor tests.

[0008] Preferably, the preprocessing and standardization of multi-source heterogeneous data includes: using a high-precision interpolation algorithm to unify seismic waveform data and meteorological data with different sampling frequencies to a preset sampling frequency; encoding and normalizing attribute data; cleaning and correcting incomplete or conflicting data; and storing all processed data in a distributed database to form a dataset.

[0009] Preferably, in step S2, the coupling model includes: A quantitative model of the influence of high-altitude, low-density atmosphere on seismic wave attenuation is established. The quantitative model adjusts the geometric attenuation term or the medium attenuation term in the traditional attenuation relationship by introducing correction factors related to altitude, air pressure, and temperature. A quantitative model is established to assess the impact of low-temperature frozen soil environment on the mechanical parameters of soil and rock. The quantitative model is constructed to consider the temperature dependence of soil and rock mechanical parameters on temperature and water content, and to establish the constitutive relationship between the freeze-thaw state of the frozen soil layer and its physical and mechanical parameters. A quantitative model for the amplification effect of complex terrain on ground motion is established. The quantitative model evaluates the local terrain effect through a high-precision digital elevation model and uses numerical simulation to analyze the ground motion response of different terrain profiles and incident wave types to obtain the terrain amplification factor. The quantitative models of the effects of low-density atmosphere, low-temperature permafrost environment, and complex topography are integrated to form a high-altitude seismic wave propagation and coupling attenuation function. The coupling function introduces a high-altitude environment correction term to dynamically adjust the seismic motion attenuation characteristics.

[0010] Preferably, the coupling attenuation function is expressed as: ; in, This is a low-density atmospheric correction function based on altitude and temperature; This is a correction function for soil and rock parameters based on temperature and moisture content; This is a terrain amplification correction function based on the digital elevation model and site shear wave velocity; , , ϵ′ represents the weighting coefficient of the corresponding correction term; ϵ′ represents the new random error term.

[0011] Preferably, the quantitative model of the influence of high-altitude, low-density atmosphere on seismic wave attenuation is determined by numerical simulation analysis of the coupled vibration of the surface medium and atmosphere at different altitudes, combined with the reflection and transmission characteristics of acoustic waves at different medium interfaces, to determine the influence of the correction factor on the seismic wave energy flux density.

[0012] Preferably, the quantitative model of the influence of the low-temperature frozen soil environment on the mechanical parameters of the soil and rock is obtained by indoor dynamic triaxial test and resonant column test to obtain the curves of the dynamic shear modulus and damping ratio of the soil and rock under different temperatures and moisture contents as a function of shear strain amplitude.

[0013] Preferably, the quantitative model of the seismic amplification effect of the complex terrain is obtained by using the spectral element method, finite difference method or boundary element method to analyze the seismic response of different terrain profiles and incident wave types, and obtaining the terrain amplification factor.

[0014] Preferably, the design of the multi-source combined ground motion scenario and simulation scheme includes constructing a simulation scenario of single-source and multi-source superposition. The simulation scenario includes the near-field superposition of adjacent sources, the synergistic effect of far-field sources, and the combined effect of background seismic activity and major fault earthquakes.

[0015] Preferably, the extraction and calculation of seismic parameters at the dam site includes: acquiring and processing seismic time history records of different points on the ground surface at the dam site; calculating peak ground acceleration, peak ground velocity, and acceleration response spectrum, velocity response spectrum, and displacement response spectrum at different frequencies and damping ratios.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This scheme constructs a unique coupled model of seismic wave propagation and attenuation under the influence of high-altitude environmental factors. This model quantitatively introduces environmental parameters such as low temperature, low air pressure and soil moisture content in high-altitude areas into the seismic wave quality factor correction mechanism, which makes up for the shortcomings of existing methods that do not adequately consider the influence of special environmental factors in high-altitude areas on the seismic wave propagation and attenuation law, and significantly improves the physical accuracy and regional applicability of ground motion simulation.

[0017] 2. This scheme precisely identifies multi-source combination modes. Through clustering algorithms based on source spatial distance, seismic time correlation, and tectonic correlation, it identifies high-risk source combination scenarios. For these combination scenarios, it accurately superimposes the seismic motion time histories generated by each source in the time domain, taking into account the phase relationship and arrival time of each seismic wave. This accurately reflects the constructive interference effect that may be generated by the superposition of different source waveforms under complex source conditions. It solves the problem that existing technologies rely only on single source results or statistical envelopes and cannot accurately capture the true response of multi-source superposition.

[0018] 3. This scheme combines high-resolution topography and geomorphology with a refined geological structure model. By embedding a three-dimensional seismic wave propagation simulator using the spectral element method or the high-order finite difference method, it can accurately handle the seismic wave scattering, focusing, and topographic amplification effects caused by complex topography and geomorphology, thus making up for the shortcomings of existing methods in simulating complex site conditions.

[0019] 4. This invention obtains the probability distribution of ground motion parameters through comprehensive ground motion simulation and statistical analysis of multiple scenarios and multiple combination modes, and determines the maximum credible ground motion parameters based on specific exceedance probabilities or design reference periods, ensuring the robustness and reliability of the evaluation results, and providing more scientific and reliable support for the safety design of dam projects in high-altitude and high-seismic areas. Attached Figure Description

[0020] Figure 1 This is a system flowchart of the present invention. Detailed Implementation

[0021] Example 1: As Figure 1 As shown, this invention provides a method for studying the maximum credible earthquake at dam sites in high-altitude, high-seismic-zone areas, aiming to address the shortcomings of existing technologies in terms of multi-objective optimization capabilities, efficiency in handling complex constraints, and model adaptability. By introducing various innovative improvement strategies, the global search capability and convergence accuracy of the particle swarm optimization algorithm are enhanced. Combined with multi-factor coupling analysis, efficient and accurate assessment of dam stability is achieved, meeting the practical needs of modern water conservancy projects.

[0022] The method for studying the maximum credible earthquake at dam sites in high-altitude, high-seismic-zone areas provided in this embodiment includes the following steps: S10: Obtain geological, seismic, topographic, and environmental characteristics data of the dam site area in high-altitude, high-seismic-zone areas.

[0023] S11, collect regional geological structure and soil and rock properties data.

[0024] Specific data collection includes: identifying the distribution of active faults, fault zone geometry, strike, dip angle, slip rate, and latest active age within the region through remote sensing image analysis, aerial photogrammetry, and on-site geological surveys. Simultaneously, combining geophysical exploration methods, the sequence structure, lithological distribution, geological interface depth, and the presence of concealed faults in the underground rock and soil masses will be thoroughly investigated. For key rock and soil masses in the dam site area, borehole sampling and indoor / outdoor tests will be conducted to obtain basic physical and mechanical parameters such as density, porosity, saturation, elastic modulus, shear modulus, Poisson's ratio, internal friction angle, and cohesion. Furthermore, the nonlinear dynamic characteristics of the rock and soil masses will also be obtained.

[0025] S12 collects historical earthquake activity and source parameter data.

[0026] By reviewing relevant literature and reports, information on felt earthquakes and instrumentally recorded earthquake events occurring in the dam site area and adjacent active tectonic zones was collected.

[0027] S13, acquire topographic and meteorological data.

[0028] Traditional methods often neglect or simplify the influence of topography and meteorological environment on seismic motion. This invention acquires a high-resolution digital elevation model of the dam site area using high-precision remote sensing data to accurately characterize micro-topographic features. Simultaneously, it collects meteorological data from multiple years of data from meteorological stations in and around the dam site area, including temperature, air pressure, humidity, precipitation, wind speed, and wind direction. Particular attention is paid to environmental parameters closely related to high-altitude climates, such as the duration of extreme low temperatures, seasonal permafrost depth, and glacier distribution and melting status. For the low-pressure environment unique to high-altitude regions, vertical pressure gradient data at different elevations are required. Furthermore, hydrogeological data for the region needs to be collected, such as groundwater depth, surface water distribution, and the distribution and thickness of any existing permafrost layers.

[0029] S14 performs preprocessing and standardization on multi-source heterogeneous data.

[0030] This step converts the heterogeneous data acquired in S11 to S13 into a unified, standardized format to facilitate subsequent model input and processing.

[0031] Preprocessing includes: for seismic waveform and meteorological data with different sampling frequencies, high-precision interpolation algorithms such as cubic spline interpolation are used to unify them to a preset sampling frequency. Attribute data is encoded and normalized; for example, lithology types are converted into numerical codes, and physical and mechanical parameters are scaled to a uniform numerical range to eliminate the impact of dimensional differences on model training. Incomplete or conflicting data is cleaned and corrected. After data standardization, all processed data is stored in a distributed database to form a dataset.

[0032] S20, construct a coupled model of high-altitude seismic wave propagation and attenuation.

[0033] This step is the core innovation of this invention, overcoming the failure of existing methods to fully consider the influence of the special environment of high-altitude areas on the propagation and attenuation of seismic waves. Traditional seismic motion attenuation models are usually based on empirical data from plains or low-altitude areas, failing to effectively reflect the comprehensive impact of high-altitude-specific factors such as low-density atmosphere, low-temperature permafrost, and complex terrain on seismic wave energy dissipation and propagation paths. This invention, through multiphysics coupling modeling, significantly improves the accuracy of seismic motion parameter prediction in high-altitude, high-seismic-region areas.

[0034] S21. Establish a quantitative model of the influence of high-altitude, low-density atmosphere on seismic wave attenuation.

[0035] This step establishes a physical model of energy conversion at the air-solid interface, quantifying how low-density atmosphere can lead to an increased difference in acoustic impedance between the surface soil and the atmosphere, potentially affecting the dissipation of surface wave energy into the air medium.

[0036] Specifically, by using meteorological data obtained from S13, correction factors related to altitude, air pressure, and temperature are introduced to adjust the geometric attenuation term or the medium attenuation term in the traditional attenuation relationship. This correction factor is then used to analyze the coupled vibrations of the surface medium and the atmosphere at different altitudes through numerical simulations, such as the finite element / finite difference method. Combined with the reflection and transmission characteristics of acoustic waves at different medium interfaces, its impact on seismic wave energy flux density is determined.

[0037] S22, Establish a quantitative model of the influence of low-temperature frozen soil environment on the mechanical parameters of rock and soil.

[0038] The strength and stiffness of soil increase significantly when frozen, while in unfrozen conditions or during thawing, it exhibits complex plasticity, creep, and pore water pressure effects.

[0039] This step involves constructing a temperature-dependent model of the mechanical parameters of the soil and rock mass, taking into account both temperature and moisture content.

[0040] Through indoor dynamic triaxial tests and resonant column tests, the dynamic shear modulus and damping ratio of soil and rock under different temperatures and moisture contents were obtained as curves of shear strain amplitude. For permafrost, constitutive relations between its freeze-thaw state and physical and mechanical parameters were established. This model uses temperature data and hydrogeological data obtained in S13 as inputs and dynamically adjusts the basic parameters of soil and rock obtained in S11 to make it more applicable in high-altitude, low-temperature or permafrost environments.

[0041] S23, Establish a quantitative model of the amplification effect of complex terrain on seismic motion.

[0042] A local topographic effect assessment model based on a high-precision digital elevation model (DEM) was established. Numerical simulation methods, such as the spectral element method, finite difference method, or boundary element method, were used to analyze seismic responses under different topographic profiles and incident wave types. A series of topographic amplification factors (TFAs) were obtained through simulation, defined as the ratio of peak ground motion (PGM) or spectral value of the ground motion under topographic conditions to that under non-topographic conditions. The model uses high-precision DEM data acquired in S13 as the main input and outputs a topographic amplification factor distribution map of each point in the dam site area, describing the calculation of the local seismic response at the dam site.

[0043] S24 integrates the influence of multiple factors to form a coupling function for the propagation and attenuation of high-altitude seismic waves.

[0044] After completing S21 to S23, the aforementioned quantization models are integrated to construct a high-altitude seismic wave propagation and attenuation coupling function that comprehensively considers the influence of low-density atmosphere, low-temperature permafrost, and complex topography. Traditional attenuation relationship: ; Where Y is a ground motion parameter such as peak ground acceleration or spectral acceleration, M is the magnitude, R is the source distance, VS is the site shear wave velocity, Vref is the reference shear wave velocity, c1 to c6 are regression coefficients, and ϵ is the random error term.

[0045] Based on this, the present invention introduces a high-altitude environment correction term to construct a new coupling attenuation function.

[0046] Specifically, for the geometric attenuation term or the medium attenuation term, the low-density atmospheric correction factor established in S21 is introduced; for the site effect term, the low-temperature permafrost correction factor established in S22 and the topographic amplification factor established in S23 are introduced. The corrected coupling attenuation function can be expressed as: ; in, This is a low-density atmospheric correction function based on altitude and temperature; This is a correction function for soil and rock parameters based on temperature and moisture content; This is a terrain amplification correction function based on the digital elevation model and site shear wave velocity; , , The weighting coefficients for the corresponding correction terms are calibrated and optimized based on measured seismic ground motion data from high-altitude areas using regression analysis or machine learning methods; ϵ′ represents a new random error term. This coupling function can dynamically adjust the seismic ground motion attenuation characteristics, accurately reflecting the seismic wave propagation patterns under the special environment of high altitudes, and is the fundamental guarantee for improving the accuracy of seismic ground motion parameter evaluation in this invention.

[0047] S30 identifies and quantifies the main seismogenic structures and potential seismic source parameters in the region.

[0048] S31, identifying potential seismogenic faults based on geological structural data.

[0049] In-depth analysis was conducted on the geological structural data collected at S11. All potentially seismically active fault structures in the region were identified using existing technologies. All identified fault structures were mapped into high-precision active tectonic maps and then classified into primary seismogenic faults, secondary active faults, and inactive faults.

[0050] S32, determine the geometric parameters and activity characteristics of the fault zone.

[0051] For each potential seismogenic fault identified by S31, precise parameter quantification is performed. For each active fault, its strike, dip angle, length, width, and burial depth are precisely determined. The maximum potential magnitude and focal depth are assessed.

[0052] S33, constructing a probabilistic model for potential seismic sources in the region.

[0053] Integrating the results from S31 to S32, a probabilistic model of regional seismic activity is constructed. By dividing all potential seismogenic faults and regional background seismic activity into different source regions or source lines, seismic activity parameters and maximum potential magnitudes are estimated for each source region / line. For background source regions, a surface source model is used to describe their uniformly distributed seismic activity; for active faults, a line source model or fault model is used. Based on this, a probabilistic model of earthquake event occurrence rate and magnitude distribution is constructed.

[0054] S40, designing and simulating multi-source combined seismic motion scenarios.

[0055] S41, delineate the focal region and define characteristic focal events.

[0056] Based on the probabilistic source model constructed using S33, the area within a certain range around the dam site is divided into several source regions or source lines with similar seismic activity characteristics. For each source region or source line, representative characteristic source events are defined. Characteristic source events typically include different magnitude levels, such as the maximum potential magnitude, the design reference magnitude, and the magnitude and epicenter location corresponding to different return periods.

[0057] S42, construct a simulation scenario of single-source and multi-source superposition.

[0058] The simulation scenarios include: 1. Near-field superposition of adjacent seismic sources: Consider that two or more active faults may generate seismic waves sequentially or simultaneously in a short period of time, resulting in a superposition effect of seismic waves at the dam site.

[0059] Second, the synergistic effect of far-field sources: Although a single far-field source has a small impact on the dam site, multiple far-field sources may produce a nonlinear superposition effect under certain conditions.

[0060] Third, the combined effect of background seismic activity and earthquakes from major faults: The ground motions generated by regional background seismic activity and those generated by major active faults are superimposed and analyzed.

[0061] S43, determine the ground motion records and physical parameters required for the simulation.

[0062] This step provides specific input data for the seismic motion simulation. Based on the simulation scenario designed in S42, the input seismic motion records used for the simulation are determined. All selected seismic motion records need to undergo baseline correction, filtering, and normalization, and ensure that they have sufficient time length and frequency bandwidth. Simultaneously, the physical parameters of the medium required for the simulation are determined, including the geomechanical parameters of the soil and rock determined in S11 and S22, such as density, shear wave velocity, Lamé constant, and damping ratio, as well as the parameters of the high-altitude attenuation coupling model determined in S24.

[0063] S44 defines the region grid and boundary conditions for the simulation calculation.

[0064] This step provides a computational framework for the numerical simulation. A three-dimensional computational domain grid is established based on the size of the dam site area, its complex terrain, and the frequency of seismic waves.

[0065] Boundary conditions are set by creating artificial boundaries at the bottom and sides of the computational domain to simulate the propagation of seismic waves from an infinite medium into a finite computational domain and to absorb reflected waves at the boundaries.

[0066] S50, based on a coupled model, performs refined simulation calculations of ground motion parameters at the dam site.

[0067] S51, a high-altitude seismic wave propagation and attenuation coupling model is used to simulate seismic wave propagation.

[0068] The high-altitude seismic wave propagation and attenuation coupling function established in S24 is embedded into the ground motion simulation software. During the simulation, based on the single-source and multi-source superposition scenarios designed in S42, the source parameters determined in S43 and the computational grid and boundary conditions determined in S44 are used as inputs. As the seismic waves propagate from the source to the dam site, the coupling model dynamically adjusts the attenuation characteristics of the seismic waves in real time.

[0069] Specifically, for regions with different elevations, the medium attenuation coefficient of seismic waves is dynamically adjusted based on the low-density atmospheric correction model established in S21; for potentially existing low-temperature permafrost layers, parameters such as shear wave velocity and damping ratio are updated based on the soil and rock mechanics parameter model established in S22; for regions with complex terrain, the energy amplification or scattering effect of seismic waves passing through terrain undulations before reaching the dam site is calculated based on the terrain amplification model established in S23. For example, the displacement field u(x,t) of seismic waves during propagation can be described by the wave equation: ; Wherein, ρ(x,T,W) is the medium density considering the effects of temperature T and water content W, C(x,T,W) is the elastic tensor considering the effects of temperature T and water content W, f(x,t) is the source term, and η(x,Alt,T) is the damping coefficient considering the effects of altitude Alt and temperature T, reflecting the energy dissipation of seismic waves under the coupling effect of high-altitude, low-density atmosphere and rock and soil.

[0070] It is important to note that the medium parameters ρ, C, and damping coefficient η in this equation are no longer constants, but rather dynamically change with the spatial location x and environmental factors T, W, and Alt. By solving this wave equation with dynamically adjusted parameters, a high-precision three-dimensional seismic wavefield of the dam site area can be obtained.

[0071] S52, Extract and calculate seismic motion parameters at the dam site.

[0072] Seismic motion time history records were obtained and processed at different points on the ground surface at the dam site. Seismic motion parameters include: 1. Peak ground acceleration (PGA): The maximum absolute value of the time history of horizontal and vertical ground motion accelerations on the Earth's surface.

[0073] Second, Peak Surface Velocity (PGV): The maximum absolute value of the time histories of horizontal and vertical ground motion velocities on the Earth's surface.

[0074] Third, response spectrum: the maximum structural response at different frequencies and damping ratios, including acceleration response spectrum, velocity response spectrum, and displacement response spectrum. Special attention is paid to high-frequency and long-period spectral values, as well as broadband spectral characteristics.

[0075] S60, comprehensively evaluate the maximum credible seismic motion parameters at the dam site and conduct uncertainty analysis.

[0076] S61 performs statistical analysis and outer envelope processing on the simulation results.

[0077] A systematic statistical analysis was conducted on the seismic motion parameters extracted and calculated by S52. Through regression analysis, empirical relationships between seismic motion parameters and parameters such as magnitude and focal distance were established to verify the rationality of the simulation results and to process the outer envelope.

[0078] S62, Considering parameter uncertainties, perform probabilistic seismic hazard analysis.

[0079] Specifically, the uncertainties in the probabilistic source model constructed in S34 and the coefficients in the high-altitude seismic wave propagation and attenuation coupling function constructed in S24 are used as inputs. The uncertainties of source parameters, such as the upper limit of magnitude, the magnitude-frequency relationship, attenuation model coefficients, and site effect parameters, are propagated using a logic tree method. For each ground motion parameter, such as peak ground acceleration (PGA) or spectral acceleration at a specific frequency, its exceedance probability curve is calculated, representing the probability of exceeding a certain threshold within a future time period. This curve integrates all potential sources, all possible magnitudes, and all possible ground motion propagation paths and attenuation characteristics, along with their respective uncertainties. This step outputs the ground motion parameter values ​​and their confidence intervals for different return periods at the dam site, such as 50-year, 500-year, and 10,000-year return periods.

[0080] S63, determine the design value of the maximum credible seismic motion parameters at the dam site.

[0081] Based on the envelope results of S61 and the probabilistic seismic hazard analysis results of S62, and taking into account the importance of the dam project, design life, safety level, and regional seismic tectonic background, the design values ​​of the maximum credible seismic motion parameters for the dam site are determined. The maximum credible seismic motion parameters typically include the design reference ground motion and the maximum investigation ground motion.

Claims

1. A method for studying the maximum credible earthquake at the dam site in a high-altitude, high-seismic-zone area, characterized in that, Includes the following steps: S1: Obtain geological, seismic, topographic and environmental characteristics data of the dam site area in high-altitude and high-seismic-risk areas, as well as historical seismic activity and source parameter data, and preprocess and standardize the data. S2: Construct a coupled model for the propagation and attenuation of high-altitude seismic waves; In step S2, the attenuation coupling model includes: A quantitative model of the influence of high-altitude, low-density atmosphere on seismic wave attenuation is established. The quantitative model adjusts the geometric attenuation term or the medium attenuation term in the traditional attenuation relationship by introducing correction factors related to altitude, air pressure, and temperature. A quantitative model is established to assess the impact of low-temperature frozen soil environment on the mechanical parameters of soil and rock. The quantitative model is constructed to consider the temperature dependence of soil and rock mechanical parameters on temperature and water content, and to establish the constitutive relationship between the freeze-thaw state of the frozen soil layer and its physical and mechanical parameters. A quantitative model for the amplification effect of complex terrain on ground motion is established. The quantitative model evaluates the local terrain effect through a high-precision digital elevation model and uses numerical simulation to analyze the ground motion response of different terrain profiles and incident wave types to obtain the terrain amplification factor. The quantitative models of the effects of low-density atmosphere, low-temperature permafrost environment, and complex topography are integrated to form a high-altitude seismic wave propagation and coupling attenuation function. The coupling attenuation function introduces a high-altitude environment correction term to dynamically adjust the seismic motion attenuation characteristics. The coupling attenuation function is expressed as: ； in, This is a low-density atmospheric correction function based on altitude and temperature; This is a correction function for soil and rock parameters based on temperature and moisture content; This is a terrain amplification correction function based on the digital elevation model and site shear wave velocity; , , These are the weighting coefficients for the corresponding correction terms; For the new random error term; S3: Identify and quantify the main seismogenic structures and potential seismic source parameters in the region, including identifying potential seismogenic faults based on geological structural data, determining the geometric parameters and activity characteristics of fault zones, and constructing probabilistic models for potential seismic sources in the region. S4: Divide the source region and define characteristic source events, construct simulation scenarios of single-source and multi-source superposition, determine the ground motion records and physical parameters required for simulation, and formulate the regional grid and boundary conditions for simulation calculation; S5: Based on the coupling model, perform refined simulation calculations of the ground motion parameters at the dam site, including embedding the high-altitude seismic wave propagation and coupling attenuation function into the ground motion simulation software, applying a multi-source combined ground motion scenario, dynamically adjusting the attenuation characteristics of the seismic waves during the propagation process, and extracting and calculating the ground motion parameters at the dam site; and comprehensively evaluating the maximum credible ground motion parameters at the dam site and performing uncertainty analysis.

2. The method for studying the maximum credible earthquake at the dam site in a high-altitude, high-seismic-zone area according to claim 1, characterized in that: The acquisition of geological, seismic, topographic, and environmental characteristics data of the dam site area in high-altitude, high-seismic-zone areas includes: collecting regional geological structure and rock and soil properties data. The collection includes identifying the distribution of active faults through remote sensing image analysis, aerial photogrammetry, and on-site geological surveys; combining geophysical exploration to detect the sequence structure, lithological distribution, geological interface depth, and hidden faults of underground rock and soil; and obtaining basic physical and mechanical parameters and nonlinear dynamic characteristics of rocks or soils through borehole sampling and indoor and outdoor tests.

3. The method for studying the maximum credible earthquake at the dam site in a high-altitude, high-seismic-zone area according to claim 1, characterized in that: The data preprocessing and standardization includes: using a high-precision interpolation algorithm to unify seismic waveform data and meteorological data with different sampling frequencies to a preset sampling frequency; encoding and normalizing attribute data; cleaning and correcting incomplete or conflicting data; and storing all processed data in a distributed database to form a dataset.

4. The method for studying the maximum credible earthquake at the dam site in a high-altitude, high-seismic-zone area according to claim 1, characterized in that, The quantitative model of the influence of high-altitude, low-density atmosphere on seismic wave attenuation is used to analyze the coupled vibration of the surface medium and atmosphere at different altitudes through numerical simulation. Combined with the reflection and transmission characteristics of acoustic waves at different medium interfaces, the influence of the correction factor on seismic wave energy flux density is determined.

5. The method for studying the maximum credible earthquake at a dam site in a high-altitude, high-seismic-zone area according to claim 1, characterized in that, The quantitative model of the influence of the low-temperature frozen soil environment on the mechanical parameters of rock and soil was obtained by indoor dynamic triaxial test and resonant column test to obtain the curves of the dynamic shear modulus and damping ratio of rock and soil under different temperatures and moisture contents as a function of shear strain amplitude.

6. The method for studying the maximum credible earthquake at the dam site in a high-altitude, high-seismic-zone area according to claim 1, characterized in that, The quantitative model of the amplification effect of complex terrain on seismic motion is used to analyze the seismic response of different terrain profiles and incident wave types using the spectral element method, finite difference method or boundary element method, and obtain the terrain amplification factor.

7. The method for studying the maximum credible earthquake at the dam site in a high-altitude, high-seismic-zone area according to claim 1, characterized in that, The simulation scenario includes near-field superposition of adjacent seismic sources, synergistic effects of far-field seismic sources, and the combined effects of background seismic activity and major fault earthquakes.

8. The method for studying the maximum credible earthquake at the dam site in a high-altitude, high-seismic-zone area according to claim 1, characterized in that, The extraction and calculation of ground motion parameters at the dam site includes: acquiring and processing ground motion time history records at different points on the ground surface at the dam site; calculating peak ground acceleration, peak ground velocity, and acceleration response spectrum, velocity response spectrum, and displacement response spectrum at different frequencies and damping ratios.

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