Palmdale Bulge and its significance

  • G. J. Lensen Geological Survey, Lower Hutt, New Zealand


As an aftermath to the 1971 San Fernando earthquake in southern California two existing levelling routes were relevelled in order to assess the amount of earth shift that triggered this earthquake. Comparison of
the new and old data revealed two important points:

(a) the 1971 earthshift resulted in a maximum uplift of 2 m on the upthrown (Transverse Ranges) side and a maximum subsidence of 110 mm on the downthrown (Los Angeles basin complex) side.

(b) prior to the 1971 earthshift the area was deforming for at least 10 years, reaching over the period 1968-69 the maximum of about 80 mm uplift in the future epicentral area.


Castle, R. O., Alt, J. N., Savage, J. C. and Balazs, E. I. 1974. "Elevation Changes Preceding the San Fernando Earthquake of February 9, 1971". Geology 2: 61-66.

Lensen, G. J. 1969. "Earth Deformation and Earthquake Prediction". Bulletin of N.Z. Nat. Soc. for Earthq. Eng., Vol. 2, No. 4.

Lensen, G. J. 1974. On the Nature of Vertical Deformation and on the Frequency of Earth Deformation in General. Tectonophysics, 23: 391-406.

Mogi, K. 1968. "Sequential Occurrences of Recent Great Earthquakes". Bull. Earthquake Research Institute, Tokyo Univ. 46: 1975-203.

Tsuboi, C. 1933. "Investigation on the Deformation of the Earth's Crust Found by Precise Geodetic Means". Japan Journal of Astronomy and Geophysics 10: 93-248.

Rikitaki, T. 1975. "Statistics of Ultimate Strain of the Earth's Crust and Probability of Earthquake Occurrence". Tectonophysics, 26, 1-21.

Reid, H. F. 1910. "The California Earthquake of April 18, 1906". 2. "The Mechanics of the Earthquake". Carnegie Institution of Washington, Washington D.C., 192 pp.

How to Cite
Lensen, G. J. (1978). Palmdale Bulge and its significance. Bulletin of the New Zealand Society for Earthquake Engineering, 11(3), 193-194.
Technical Notes