Underground explosion equivalent estimation method based on Lg wave seismic moment

Abstract

The invention relates to an underground explosion equivalent estimation method based on Lg wave seismic moments, which comprises the following steps: aiming at a specific region, carrying out theoretical seismic map simulation and inverting an Lg wave Q value by utilizing a frequency-wave number integration method, inverting an Lg wave seismic moment source on the basis, calibrating the relationship between the Lg wave seismic moment source and the seismic moments, and combining the Lg wave seismic moments obtained by observing data inversion and a seismic source model to estimate the underground explosion equivalent. An equivalent estimation method based on Lg wave seismic moments can be established; according to the method, the advantage that the Lg wave seismic moment can be quickly inverted through the source frequency spectrum relative to the source seismic moment is fully utilized, the underground explosion equivalent is quickly estimated by pre-calibrating the relationship between the two different sites and combining the seismic source model, and the calibration result considers different seismic source type combinations and is suitable for various conditions; when the Lg wave seismic moment inversion equation is solved, an L-M algorithm is adopted, a hysteresis factor is introduced, non-convergence during solving is avoided, and the stability of the algorithm is improved. And rapid estimation of the underground explosion equivalent in a specific region is realized.

Description

Technical Field

[0001] The invention belongs to the technical field of earthquake monitoring, and in particular relates to an underground explosion equivalent estimation method based on Lg wave seismic moment. Background Art

[0002] Equivalent estimation is an important part of earthquake monitoring verification. Currently, the commonly used equivalent estimation methods include magnitude-equivalent relationship based on statistical results, network average P-wave spectrum method based on source model, and amplitude spectrum inversion based on regional seismic phase. Among them, the amplitude spectrum inversion method obtains the seismic moment of the event based on the amplitude of the Pn wave or Lg wave phase, and estimates the equivalent by combining the seismic moment-equivalent relationship in the source model. Since the reduced displacement potential in the source model is essentially the distance-normalized Pn wave displacement potential, the Pn wave seismic moment can be directly substituted into the classic source model for equivalent estimation. However, in practice, the Pn wave amplitude is greatly affected by the radiation pattern in different directions. Therefore, the source seismic moment obtained by Pn wave inversion has a large dispersion, and the general source seismic moment inversion method requires a long time to invert because of the calculation of Green's function, which is not conducive to the formation of real-time rapid reporting capabilities. Summary of the invention

[0003] The present invention provides an underground explosion equivalent estimation method based on Lg wave seismic moment, and the technical problem to be solved is: realizing rapid estimation of underground explosion equivalent.

[0004] In order to solve the above technical problems, the present invention provides a method for estimating underground explosion equivalent based on Lg wave seismic moment, which is characterized by comprising the following specific steps:

[0005] Step 1: Invert the Lg wave quality factor Q value of a specific area as the medium parameter input when inverting the Lg wave seismic moment M0(Lg);

[0006] Step 2: simulate the theoretical waveforms under different conditions, use the Lg wave source spectrum inversion method to invert the Lg wave seismic moment M0(Lg), calibrate the relationship between the source seismic moment M0(s) and the Lg wave seismic moment of different sites, and obtain the ratio of the two M0(Lg) / M0(s);

[0007] Step 3: Preprocess the actual monitoring waveform data and use the spectrum inversion method to obtain the M0(Lg) of the underground explosion as the input for the next step of equivalent estimation;

[0008] Step 4: Calculate M0(s) based on the ratio of M0(Lg) / M0(s) in step 2 and M0(Lg) obtained in step 3, and estimate the underground explosion equivalent in combination with the earthquake source model and source area medium parameters.

[0009] Beneficial effects: The present invention uses the frequency-wavenumber integration method to simulate theoretical seismic maps and invert the Lg wave Q value for specific areas. On this basis, the Lg wave seismic moment source is inverted and its relationship with the seismic moment is calibrated. The Lg wave seismic moment and source model obtained by inverting the observed data can be combined to establish an equivalent estimation method based on the Lg wave seismic moment, which is of great significance to improving my country's underground explosion equivalent estimation technical means and enhancing the ability to process, analyze and judge earthquake monitoring data.

[0010] The present invention makes full use of the advantage that the Lg wave seismic moment can be quickly inverted through the source spectrum relative to the source seismic moment. By pre-calibrating the relationship between the two in different sites and combining the source model, the rapid estimation of the underground explosion equivalent is achieved. The advantages are as follows:

[0011] (1) Combining theoretical seismogram simulation and Lg source spectrum inversion method, the M0(Lg) / M0(s) relationship was calibrated for different sites combined with regional medium models, and the ratio of the two was obtained. The calibration result takes into account different combinations of seismic source types and is applicable to a variety of situations.

[0012] (2) The LM algorithm was used to solve the Lg wave seismic moment inversion equation, and a hysteresis factor was introduced to avoid non-convergence during solution and improve the stability of the algorithm.

[0013] (3) Combined with the earthquake source model, a method for estimating underground explosion equivalent based on Lg wave seismic moment was established, which realized the rapid estimation of underground explosion equivalent in specific areas. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 is a flow chart of an embodiment of the present invention.

[0015] Figure 2 This is a theoretical seismogram waveform simulated in an embodiment of the present invention.

[0016] Figure 3 These are the calibration results of M0(Lg) / M0(s) for different sites obtained in the embodiments of the present invention.

[0017] Figure 4 This is the result of inverting the Lg wave seismic moment using the data from various stations in a certain experiment in an embodiment of the present invention. DETAILED DESCRIPTION

[0018] In order to make the purpose, content and advantages of the present invention more clear, the specific implementation methods of the present invention are further described in detail below.

[0019] The present invention proposes a method for estimating underground explosion equivalent based on Lg wave seismic moment, and the specific steps are as follows:

[0020] Step 1: Use theoretical seismogram simulation and double-station method to invert the Lg wave quality factor Q value of a specific area, which is used as the medium parameter input when inverting the Lg wave seismic moment M0(Lg);

[0021] (1.1) Using the wave number-frequency integration method to simulate the theoretical waveform, set the pure ISO, bury depth 0.36km, simulate the theoretical seismogram at the epicenter distance of 400-700km, and use the Lg wave intercepted by the velocity window of 3-3.5km / s, as shown in Figure 2 As shown;

[0022] (1.2) Pair the stations at different epicentral distances, and calculate the amplitude spectrum ratio of each station pair. To ensure the accuracy of the results, superimpose the five groups of displacement spectrum ratios at the corresponding frequencies and take the average, and use the fitting formula to calculate the Q value.

[0023] Step 2: simulate the theoretical waveforms under different conditions, use the Lg wave source spectrum inversion method to invert the Lg wave seismic moment M0(Lg), calibrate the relationship between the source seismic moment M0(s) and the Lg wave seismic moment of different sites, and obtain the ratio of the two M0(Lg) / M0(s);

[0024] Different source combinations are set, and theoretical seismograms are simulated in combination with medium models in different regions. The Lg source spectrum is further used to invert the seismic moment. The LM algorithm is introduced in the inversion to ensure the convergence of the results. The specific implementation method is as follows:

[0025] (2.1) Assume that the explosion equivalent is 10kt, 100kt, 1000kt and 10000kt respectively, and take the proportional burial depth as 120m / kt 1 / 3 The corresponding burial depths are calculated to be 0.26km, 0.6km, 1.2km and 2.6km respectively. The corresponding seismic moments are obtained according to the DJ91 model and the source medium parameters in different regions. The frequency-wavenumber integration software package is used to simulate the theoretical seismogram.

[0026] (2.2) The Lg waveform is intercepted according to the Lg wave velocity window of 3-3.5 km / s, and then a 4096-point fast Fourier transform is performed. After 10 points are smoothed, the displacement spectrum is obtained, and the seismic moment is inverted according to the following formula:

[0027]

[0028] Where A(f) is the Lg wave displacement spectrum, S(f) is the source spectrum, is the epicentral distance, X(f) represents the site effect, r(f) is the random interference, G represents the geometric diffusion and Δ0 is the reference distance, which can be 100 km, v is the Lg wave group velocity, Q(f) = Q0f η, Q0 is the quality factor on the propagation path at 1Hz, η is the frequency index, and f is the frequency point.

[0029] (2.3) Taking the logarithm of the above formula, for a specific event, we can obtain the error between the Lg spectrum actually observed at the i-th station at the j-th frequency sampling point and the theoretical value:

[0030]

[0031] Using the above formula, the inversion problem is transformed into the parameter solution The optimal solution is such that the error d ij Minimum, that is, solve the following equation (Δ represents the difference between each iteration and the previous step result):

[0032] -GΔm=Δd ij

[0033] Among them, fc is the source corner frequency, G is the partial derivative matrix of the displacement spectrum with respect to the four parameters, and for earthquake events:

[0034]

[0035] Using the Levenberg-Marquardt method, the damping factor λ is introduced when solving the above equation, so that:

[0036] Δm=-(G T G+λI) -1 G T Δd

[0037] This prevents the solution of the equation from not converging.

[0038] (2.4) Using the M0(Lg) obtained above, calculate the M0(Lg) / M0(s) ratio and calibrate it for different sites.

[0039] Step 3: Preprocess the actual monitored waveform data, including removing the mean, removing the linearity, and removing the instrument response, and use the spectrum inversion method to obtain the Lg wave seismic moment M0(Lg) of the underground explosion;

[0040] For the actual observed data, repeat the M0(Lg) inversion method in step 2 to obtain the M0(Lg) of the underground explosion, which serves as the input for the next step of equivalent estimation.

[0041] Step 4: Calculate M0(s) based on the ratio of M0(Lg) / M0(s) in step 2 and M0(Lg) obtained in step 3, and estimate the underground explosion equivalent in combination with the source model and source area medium parameters to achieve rapid estimation of the underground explosion equivalent based on the Lg wave seismic moment.

[0042] According to the M0(Lg) / M0(s) relationship calibrated in different sites, the relationship between M0(Lg) and equivalent is established in combination with the earthquake source model, and the rapid estimation of underground explosion equivalent based on Lg wave seismic moment is realized. The specific implementation method is as follows:

[0043] (4.1) Filter out the actual observation data of stations with epicenter distances within the range of 4°-15°, process the data, and calculate M0(Lg) of the underground explosion according to the method in step 2.

[0044] (4.2) Combined with the M0(Lg) / M0(s) relationship given in step 3, use M0(Lg) to calculate M0(s), and convert M0(s) into the steady-state value of the equivalent displacement potential It satisfies the following relationship with M0(s):

[0045] Where α is the longitudinal wave velocity.

[0046] get Then, substitute the following earthquake source model to calculate the equivalent, and the medium parameters in the model are the medium parameters of the source area:

[0047] where β, ρ, and h are the shear wave velocity, medium density, and burial depth in the source region, respectively.

[0048] Figure 2 This is the waveform of the theoretical seismogram simulated in the embodiment of the present invention. Pure ISO is set. When the burial depth is 0.36 km, the theoretical seismogram at the epicentral distance of 400-700 km, the red color is the intercepted Lg wave, and the velocity window is 3-3.5 km / s.

[0049] Figure 3 These are the calibration results of M0(Lg) / M0(s) for different sites obtained in the embodiments of the present invention. It is assumed that ISO+CLVD+DC sources exist simultaneously, the relative intensity of DC source / ISO source is 0.3, and the relative intensity of CLVD source / ISO source is represented by K value, which is 1, 1.5, and 2 respectively. Corresponding to different curves in the figure, the horizontal axis corresponds to different equivalents and burial depths, and the vertical axis is M0(Lg) / M0(s).

[0050] Figure 4 This is the result of inverting the Lg wave seismic moment using the test station data of a certain year in an embodiment of the present invention. The dotted line is the actually observed Lg wave spectrum, the black solid line is the theoretical spectrum calculated by multiple iterations in the solution, and the red line represents the optimal solution.

[0051] The present invention makes full use of the advantage that the Lg wave seismic moment relative to the source seismic moment can be quickly inverted through the source spectrum, and realizes the rapid estimation of the underground explosion equivalent by pre-calibrating the relationship between the two in different sites and combining the earthquake source model.

[0052] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for estimating underground explosion equivalent based on Lg wave seismic moment, characterized in that: The specific steps include: Step 1: Invert the Lg wave quality factor Q value of a specific area as the medium parameter input when inverting the Lg wave seismic moment M0(Lg); Step 2: simulate the theoretical waveforms under different conditions, use the Lg wave source spectrum inversion method to invert the Lg wave seismic moment M0(Lg), calibrate the relationship between the source seismic moment M0(s) and the Lg wave seismic moment of different sites, and obtain the ratio of the two M0(Lg) / M0(s); Step 3: Preprocess the actual monitoring waveform data and use the spectrum inversion method to obtain the M0(Lg) of the underground explosion as the input for the next step of equivalent estimation; Step 4: Calculate M0(s) based on the ratio of M0(Lg) / M0(s) in step 2 and M0(Lg) obtained in step 3, and estimate the underground explosion equivalent in combination with the earthquake source model and source area medium parameters.

2. The underground explosion equivalent estimation method based on Lg wave seismic moment according to claim 1 is characterized in that: The Lg wave quality factor Q value in a specific area is inverted using theoretical seismogram simulation and the double-station method.

3. The underground explosion equivalent estimation method based on Lg wave seismic moment according to claim 2 is characterized in that: The wave number-frequency integration method is used to simulate the theoretical waveform, and the double station method is used to invert the Lg wave Q value, which is considered to be uniform within each epicentral distance range.

4. The underground explosion equivalent estimation method based on Lg wave seismic moment according to claim 1 is characterized in that: In step 2, different source combinations are set, and theoretical seismograms are simulated in combination with medium models in different regions. The Lg source spectrum is further used to invert its seismic moment, and the LM algorithm is introduced in the inversion to ensure the convergence of the results.

5. The underground explosion equivalent estimation method based on Lg wave seismic moment according to claim 4 is characterized in that: In step 2, the Lg waveform is intercepted according to the Lg wave velocity window of 3-3.5 km / s, and then a fast Fourier transform is performed to obtain the displacement spectrum. The displacement spectrum is sampled with a sampling frequency band of 0.2-3.6 Hz, and the seismic moment is inverted according to the following formula: Where A(f) is the Lg wave displacement spectrum, S(f) is the source spectrum, is the epicentral distance, X(f) represents the site effect, r(f) is the random interference, G represents the geometric diffusion and Δ0 is the reference distance, which can be 100 km, v is the Lg wave group velocity, Q(f) = Q0f η , Q0 is the quality factor on the propagation path at 1Hz, and η is the frequency index.

6. The underground explosion equivalent estimation method based on Lg wave seismic moment according to claim 5 is characterized in that: Taking the logarithm of the above formula, for a specific event, we can obtain the error formula between the Lg spectrum actually observed at the i-th station at the j-th frequency sampling point and the theoretical value: Using the error formula, the inversion problem is transformed into the problem of finding the parameter m = [M0 Lg ,Q0,f c ,η], so that the error d ij Minimum, that is, solve the following equation: -GΔm=Δd ij Where fc is the source corner frequency, and G is the partial derivative matrix of the displacement spectrum with respect to the four parameters.

7. The underground explosion equivalent estimation method based on Lg wave seismic moment according to claim 6 is characterized in that: The Levenberg-Marquardt algorithm is used to solve the Lg wave seismic moment inversion equation, and the damping factor λ is introduced, so that: Δm=-(G T G+λI) -1 G T Δd This prevents the solution of the equation from not converging.

8. The underground explosion equivalent estimation method based on Lg wave seismic moment according to claim 1 is characterized by: In step 3, the M0(Lg) inversion method in step 2 is repeated for the actual observed data as the input for the next step of equivalent estimation.

9. The underground explosion equivalent estimation method based on Lg wave seismic moment according to claim 1 is characterized in that: The specific implementation of step 4 is as follows: (1) Screen out the actual observation data of stations with epicenter distances within the range of 4°-15°, process the data, and calculate M0(Lg) of the underground explosion according to the method in step 2; (2) Combined with the M0(Lg) / M0(s) relationship given in step 3, use M0(Lg) to calculate M0(s), and convert M0(s) into the steady-state value of the equivalent displacement potential It satisfies the following relationship with M0(s): Where α is the longitudinal wave velocity, ρ is the density of the source medium; get Then, substitute it into the earthquake source model to calculate the explosion equivalent.

10. The underground explosion equivalent estimation method based on Lg wave seismic moment according to claim 8, characterized in that: The earthquake source model is: The medium parameters in the model are taken from the medium parameters of the source area, where β, ρ, and h are the shear wave velocity, medium density, and burial depth of the source area, respectively.

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