Hi Kate. Not sure if this is what your looking for. These are just two of the articles from the Stanford University. The first one deals with Slow Precursors and the second with Slow Earthquakes/Tsunamis. Take Care…Don in creepy town.

Slow Precursors
JordanJ[1991]Jdeveloped a formalism for detecting slow precursors to earthquakes based on observations of the Earth's free oscillations. He derived an inequality that states that an earthquake must be precursive (non-zero moment release before the high-frequency origin time) if the characteristic duration of the moment-rate function is greater than a simple expression involving the skewness of the moment-rate function and the centroid time shift. Jordan [1991] found no evidence for a precursor to the 1989 Loma Prieta, California earthquake; however he did find evidence for a slow precursor to the April 12, 1983 Peru-Bolivia earthquake and speculated that slow precursors might be related to the silent earthquakes proposed by Beroza and Jordan [1990].

Ihmlé et al. [1993] found evidence in the free oscillation spectra of the 1989 Macquarie Ridge earthquake for a slow precursor with a time scale greater than 100s and a moment magnitude of 7.6. The observation that lead to this conclusion was a large characteristic duration and small values of the time shift spectrum at frequencies less than about 6 milliHz. Ihmlé et al. [1993] also demonstrated that it was possible that a precursor could have been smooth enough not to be detected at higher frequencies. Kedar et al. [1994] studied isolated normal-mode peaks for this earthquake that were specifically selected to be free of strong coupling effects. They found large amplitude anomalies suggesting that the earthquake was about 50% larger than indicated by surface-wave analysis [ Satake and Kanamori, 1990]. Kedar et al. [1994] argued that the phase and possibly the amplitude anomalies could be due to finite source effects, rather than a slow precursory event.

Slow Earthquakes
There were several interesting developments in the area of slow or tsunami earthquakes. Pelayo and Wiens [1990,1992] studied several tsunami earthquakes and found double-couple mechanisms with long source durations for each of them. These shallow earthquakes occurred underneath accretionary prisms in Peru and the Kurile Islands. Pelayo and Wiens [1990] favored relatively slow rupture propagation along the basal decollemont of the accretionary prism as the explanation for the slow nature of these earthquakes rather than earthquake triggered slumping, which has been proposed as the source of many tsunami earthquakes.

Kanamori and KikuchiJ[1993] and Ide et al. [1993] studied the 1992 Nicaragua earthquake, which caused a large and destructive tsunami with a local amplitude of 10 m on the Nicaraguan coast. This earthquake occurred in an area with no accretionary prism. The occurrence of this earthquake led Kanamori and Kikuchi [1993] to argue that there may be two types of tsunami events, those that arise from slow rupture, which they attribute to the effect of subducted sediments within the subduction interface, and tsunami earthquakes such as the 1896 Sanriku and 1946 Unimak Islands earthquakes, which may involve large-scale slumping. Tsunamis from the Sanriku and Unimak Islands events were extremely destructive and hence the mechanism behind their tsunami generation is quite important; however, the evidence that these tsunamis were caused by submarine slumping remains indirect.

Kanamori and Hauksson [1991] identified a slow earthquake that occurred on January 31, 1991 in shallow sediments of the Santa Maria Basin, California. Because this event radiated substantial waves at several seconds period, they concluded that large earthquakes rupturing across such sedimentary basins might excite large long period waves from slip at shallow depths.

Shearer [1994] applied a matched filter, earthquake detection algorithm to 11 years of continuous very long period IDA (International Deployment of Accelerometers) data. He detected 32 events previously unidentified by the National Earthquake Information Center in their Preliminary Determination of Epicenters catalog, nearly all of which were events on transform faults in the southern oceans. These events may have been previously undetected because they were moderate-sized events that occurred in a remote area. Shearer [1994] also identified 40 probable slow earthquakes and found like Beroza and Jordan [1990] that most were on oceanic transform faults. Unlike Beroza and Jordan [1990], Shearer [1994] did not find any events that might be characterized as ``silent'' that is, without a detectable high-frequency signature. This might be attributable to the somewhat higher frequencies that he used.

• Seismic Source Modeling