Relationships of earthquakes (and earthquake-associated mass movements) and polar motion as determined by Kalman filtered, very-long-baseline - interferometry group delays

A Kalman filter was designed to yield optimal estimates of geophysical parameters from Very-Long-Baseline-Interferometry (VLBI) group delay data. The geophysical parameters estimated were: polar motion components, adjustments to nutation in obliquity and longitude, and a change in length of day parameter. VLBI clock parameters and atmospheric zenith delay parameters were simultaneously estimated with the geophysical parameters. The primary source of VLBI group delay observations was the 1984-1986 IRIS (International Radio Interferometric Surveying) data set, consisting of day long VLBI observing sessions (made at five day intervals). The Kalman filter limits subjectivity in VLBI data analysis. The scientific objective of Kalman filtering the VLBI data was to examine the effects of earthquakes (and associated mass movements) on the polar motion of the earth. Several great earthquakes occurred during 1984-1986, all with magnitudes (M{dollar}sb{lcub}rm s{rcub}{dollar}) approaching 8.0 or above. Kalman filter runs were made for VLBI data sets surrounding (within a 45 window) the 1985 great Chilean earthquake and the 1985 Michoacan, Mexico earthquake.; A kink in polar motion coincides well with the 1985 Mexican earthquake; the associated excitation results indicate non-significant excitation at the one-sigma error level. A polar motion kink is observed about 15 days prior to the 1985 Chilean earthquake and a kink is seen 15 days after the earthquake. These kinks appear to coincide well with epochs at which earthquake swarms (in the Chilean region) begin to occur and subside. The net excitation change due to the pre- and post-seismic (Chilean) kinks is about 2.4 {dollar}pm{dollar} 0.5 mas. IRIS polar motion estimates around the time of the 1986 Taiwan earthquake were deconvolved to examine the excitation associated with this earthquake. A polar motion kink coincides directly with the Taiwan event. The net excitation change seen at the time of the Taiwan earthquake is approximately 3.8 {dollar}pm{dollar} 0.5 mas.; Earthquakes, lithospheric slab movements, lithospheric flexure near subduction zones, aseismic fault slip, etc., are believed to contribute to the polar motion excitation budget.