Analyzing stress drops of earthquakes near Wellington, New Zealand
Stress drop studies analyze the change of stress across faults before and after an earthquake. The goal of this study was to determine how stress drop varies throughout the Wellington region of the North Island of New Zealand. To the east of the North Island, the Hikurangi Trough obliquely subducts the Pacific Plate beneath the younger Australian Plate. Toward the southern end of the North Island and into Cook Strait the Pacific plate becomes more buoyant and the plate interface displays strong coupling as subduction diminishes into the strike-slip Marlborough fault system. Subduction of the Pacific plate ceases beneath the South Island and plate motion is taken up along the dextral Alpine Fault. The focus of the study centered on the locked zone of the plate interface extending from Upper Hutt to Cook Strait. Here slow slip events occur downdip of this strongly coupled zone. The study utilizes an empirical Green's function technique to estimate stress drops of earthquake sequences. A deconvolution code removes the path and instrumentation effects. Earthquakes were carefully selected in order to ensure low noise levels and precise estimations of event corner frequencies. Stress drops were calculated based on the corner frequencies and moment magnitudes of the earthquakes chosen. High stress drops were associated with earthquakes within the subducting Pacific plate in the Upper Hutt area. Events occurring in 2004/2005 had an average stress drop of ∼1,000 MPa. This was 1-2 orders of magnitude higher stress drops than events occurring in 2006 (∼13 MPa) and 2011 (∼18.4 MPa) within the same region. The Upper Hutt events were also 1-2 magnitudes higher than the Cook Strait events in 2013-2014. This suggests the slow slip event occurring in 2003 may have more strongly perturbed stresses in the locked zone than a similar event occurring in 2013-2014.
Barnes, Kyle Eugene, "Analyzing stress drops of earthquakes near Wellington, New Zealand" (2014). ETD Collection for University of Texas, El Paso. AAI1564662.