RU2451305C1 - Microseismic zoning method - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: records recorded in areas with close round conditions, magnitude values, depth of expected seismic focus and epicentral distances are selected, and an adjustment is made to the selected records in accordance with the value of the absorption factor of seismic waves for the given region and by recalculating the amplitude of vibrations at the given epicentral distance, the increment of seismic intensity (magnitude) for areas with typical ground conditions of the territory is determined in points.

EFFECT: high accuracy of determining increment of seismic intensity under strong earthquake conditions.

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Description

The invention relates to the field of seismology and engineering seismology, and in particular to methods for assessing the intensity of tremors taking into account the seismic situation of the area and the properties of the soils that make up the construction site.

A known method for determining seismicity by the method of engineering-geological analogies (IGA) [Recommendations for seismic micro-zoning in engineering surveys for construction / PNIIIS. - M., 1985. - 73 p.].

However, in the known method there is no instrumental assessment of the increment of the score (intensity) in the conditions of real strong earthquakes

The closest technical solution is the method in which the increment of seismic intensity is determined by the records of earthquakes [Zaalishvili VB Physical fundamentals of seismic micro-zoning / OFPP RAS. - M., 2000. - 367 p.].

The disadvantage of this prototype method is the inadequate consideration of the manifestation of nonlinear properties in soils when using the parameters of records of weak earthquakes, when such phenomena are almost invisible and there is no possibility of taking them into account due to the fact that the registration of strong earthquakes requires very long observation periods, which generally exclude obtaining the necessary data, which reduces the accuracy of determining the increment of point (intensity).

EFFECT: increased accuracy of determination of seismic intensity increments caused by strong earthquakes.

The technical solution is achieved by the fact that for the studied and reference (represented by average ground conditions for this area) areas with background or initial seismicity attributed to average ground conditions, records recorded in areas with similar ground conditions and values are selected from the database of records of strong earthquakes magnitudes, focal depths of expected earthquakes and epicentral distances, and a correction is entered into the selected records in accordance with the value of the absorption index seismic waves for a given area and recalculation of the oscillation amplitude by a predetermined distance determined by the increment epicenter seismic intensity (seismic intensity).

The method is as follows.

Let it be necessary to evaluate the increment of seismic intensity (scoring) for two sections in the city of Vladikavkaz, the first of which is composed of clay soils with a thickness of 6 meters, lined with boulders and pebbles, the second is composed of clay soils with a thickness of up to 20 meters, including subsidence soils (Fig. 1) . The epicenter distance for the expected earthquake (distance to the active fault) is Δ = 10 km (Vladikavkaz fault, Fig. 2).

Stations located in areas with similar ground conditions were selected from the database of strong movements. The ground conditions of stations KGS001 and KGS004 of the K-NET network (Japan) are shown in Fig. 3. The soil conditions of station KGS001 are characterized by the presence of clay soils with a thickness of about 8 m, underlain by pebbles, which made it possible to choose this station as equivalent to section 1. Station KGS004 was chosen as equivalent to section 2 due to the presence of sandy and clay soils with a thickness of about 20 m. Sands, present in the section, under conditions of strong impact on their seismic properties are close to the clay of fluid consistency, present in the section section 1.

The selected stations simultaneously recorded a seismic event on March 26, 1997 (17:31:00 GMT), with a magnitude of M = 6.3 (Fig. 4).

The oscillation amplitudes are:

Section 1 (station KGS001) - A _max1 = 129 gal (epicentral distance Δ ₁ = 30 km);

Section 2 (station KGS004) - А _max2 = 293 gal (epicentral distance Δ ₂ = 19 km).

Recalculation of the amplitude of oscillations A ₁ at a given epicentral distance Δ _{2 is} carried out according to the well-known formula:

where A ₁ and A ₂ are the oscillation amplitudes at epicentral distances Δ ₁ and Δ ₂ , respectively

α is the absorption coefficient;

e = 2.7 is the base of the natural logarithm.

Using the absorption coefficient α, for our conditions it is α = 0.0196 (km ^-1 ), and recounting the maximum acceleration amplitude for the epicentral distance from the Vladikavkaz fault Δ = 10 km, we obtain the amplitude of the acceleration oscillations in both sections:

Section 1-A _{max 1} (10 km) = 129 · e ^{-0.0196 · (10-30)} = 191 (gal);

Section 2-A _{max 1} (10 km) = 293 · e ^{-0.0196 · (10-19)} = 350 (gal).

Further, using the above formula, we calculate the increment of the score (intensity) for the soil conditions of section 2 with respect to section 1 for the same distance, which will be:

The main parameters used in the calculations and the calculation data are summarized in table 1.

Table 1 Calculation of the increment of points Station code Station Equivalent Δ, km A _max , gal A _max (Δ = 10 km), gal The increment ΔI relative to KGS001 KGS001 Plot 1 thirty 129 191 0 KGS004 Plot 2 19 293 350 0.87 Note: magnitude of the earthquake M = 6.3; focal depth h = 8 km.

The proposed method allows, based on the use of oscillation amplitudes of real records of strong earthquakes, to significantly increase the accuracy of determining the increment of seismic intensity (scoring) on typical soils of the study area.

Claims (1)

A method of seismic micro-zoning, including the assessment of seismic intensity determined from earthquake records, characterized in that for the studied and reference (represented by average ground conditions for this area) sections with background or initial seismicity referred to average ground conditions, from the database of records of strong earthquakes records are selected that are recorded in areas with similar ground conditions, magnitudes, focal depths of expected earthquakes and epicenter nymi distances to selected records a correction in accordance with the magnitude of the absorption coefficient of the seismic waves for a given area and recalculation of the oscillation amplitude by a predetermined distance determined by the increment epicenter seismic intensity (seismic intensity).

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