Salih Faizi, 70, an authority on the geology of the Soviet Union for the U.S. Geological Survey, died Tuesday at Sibley Memorial Hospital where he was being treated for cancer.

During his 48 years as a geologist in Russia, Germany and this country, Dr. Faizi had specialized in the study of environmental factors affecting the vulnerability of foundations to destruction by seismic waves, either natural or artificial, and the detection of underground nuclear testing.

He also an authority on crystallography and mineralogy, and the physical and chemical properties and behavior of geologic subjects and the early physical and geographic history of man and his environment.

After joining the U.S. Geological Survey in 1961, Dr. Faizi worked in military geology, helping to appraise the mineral resources of the Soviet Union, including uranium deposits, he also studied the geological aspects of the detection of underground nuclear testing, and translated current earth science literature. He was considered an expert on the climatic history of Soviet Central Asia and Kazakhstan.

He received two superior performance awards and a letter of commendation for his work in engineering geology for the survey.

Born in Kazan, in the Soviet Union, Dr. Faizi studied geology and mining at the Polytechnic Institute of Novocherkassk, in the U.S.S.R. and earned a bachelor's degree in 1932. In 1949, he earned a doctorate in geology from the University of Freiburg in West Germany and was a research geologist with the university's Mineralogical Institute in 1950-51.

He was a geologist with the Geological Adminstraton of Eastern Siberia from 1932 to 1936, and a senior research geologist with the Scientific Research Institute for Gold Deposit in Moscow.

During World War II, he was a captain in the Soviet Army, serving as a military engineer. Captured and held a prisoner of war in Germany, he later studied and worked there before immigrating to this country in 1951.

Dr. Faizi then worked as a translator and script writer for the old U.S. Information Agency; was a field geologist in this country and in Canada for the National Lead Co., and an asistant editor for crystallography for the McGraw Hill publishing company before joining the geological survey.

He lived in Washington and was a member of the American Association for the Advancement of Science and the Geological Society of Washington.

Survivors include his wife, Hilda, a son, Edgar, and a daughter, Sarah, all of Washington.