Seismic Microzoning

Seismic Microzoning 

a branch of engineering seismology whose objective is to refine seismic zoning data and to determine precisely the degree of earthquake danger in regions being built up.

By means of seismic microzoning, the intensity of earthquakes in units as given on maps of seismic zones may be corrected ± 1–2 units depending on local tectonic, geomorphological, and ground conditions.

Techniques for evaluating the relative resonance characteristics of the ground are the most highly developed. They make it possible to conduct direct instrument observations in different sectors of the territory under study. The seismic intensity rating is greatly influenced by the flooding of rocks (the water table), the lithological composition of rocks and the temperature of permafrost, the homogeneity and bedding conditions of types of ground, and the character of the relief (the presence of steep slopes also increases seismic intensity). As a rule, seismic intensity is lowered one degree on rocky ground and permafrost and raised one degree on friable and, in particular, moist ground.

According to the Construction Code (part II, section A, chapters 12–69) seismic microzoning maps of construction areas must be consulted when designing earthquake-resistant structures.

REFERENCES

Medvedev, S. V. Inzhenernaia seismologiia. Moscow, 1962.
Rekomendatsii po seismicheskomu mikroraionirovaniiu. Moscow, 1971.
Seismicheskoe mikroraionirovanie, fasc. 1. Dushanbe, 1973.
Vliianiegruntov na intensivnost’seismicheskikh kolebanii. (Voprosy inzhenernoi seismologii, issue 15.) Moscow, 1973.

S. A. FEDOROV