![]() ![]() Because of this relationship, we can plot the data on a log/log scale (1). ![]() In other words, the declining rate of aftershocks can be graphed as a curve that falls steeply at first and then levels off gradually without ever quite reaching zero. Mathematically speaking, the decrease is logarithmic and asymptotic. ![]() This is a defining characteristic of all mainshock-aftershock sequences. When we look at plots showing the number of magnitude 3 and larger earthquakes each day, we can see that those daily counts start high and decrease rapidly. Because people mostly want to know when they will stop feeling aftershocks, we’ll estimate when we expect a return to background level for earthquakes greater than magnitude 3. We usually say that aftershocks have stopped when the seismicity in the ruptured area returns to its background level, which is the average rate of earthquakes prior to the mainshock. ![]() The article, "Consecutive Ruptures on a Complex Conjugate Fault System During the 2018 Gulf of Alaska Earthquake," was published in Scientific Reports at DOI: 10.The burning question on the minds of many residents in Southcentral Alaska is, “When will the aftershocks stop?” This is a tricky question, but enough time has passed since the November 30 magnitude 7.1 earthquake for us to make an informed estimate. This method represents a promising step forward in modeling earthquake rupture processes in complex fault systems based only on seismic body waves, which may improve modeling of seismic wave propagation and mapping of complex fault networks in tectonically active areas. "Our findings show that irregular rupture stagnation 20 kilometers north of the earthquake's epicenter may have been promoted by a fault step across the seafloor fracture zone," explains co-author Assistant Professor Ryo Okuwaki, "They also indicate a causal link between rupture evolution and pre-existing bathymetric features in the Gulf of Alaska." These features caused discontinuities in the fault geometry that led to irregular rupture behavior. "Our model further suggests that this rupture tended to occur along weak zones in the sea floor: fracture zones that extend east-west, as well as plate-bending faults that run parallel to north-south-oriented magnetic lineaments." "Our results confirm previous reports that this earthquake ruptured a conjugate fault system in a multi-shock sequence," says study first author Shinji Yamashita. The main rupture stage of the earthquake, which lasted for 27 seconds, affected fault segments oriented both north-south and east-west. This approach allows us to analyze seismic P waves and estimate the focal mechanisms and rupture evolution of geometrically complex earthquakes involving rupture of multiple fault segments."īased on the distribution of aftershocks within one week of the main shock of the Gulf of Alaska earthquake, this method was applied to represent slip along a horizontal plane at a depth of 33.6 km. They then applied this method to the magnitude 7.9 earthquake that struck the Gulf of Alaska near Kodiak Island on January 23, 2018.Īs study co-author Professor Yuji Yagi explains, "Our method uses a flexible finite-fault inversion framework with improved smoothness constraints. In a new study published in Scientific Reports, a research team led by the University of Tsukuba developed a new method to model the details of complex earthquake rupture processes affecting systems of multiple faults. Of course, given the complexity of the environments where these ruptures typically occur, the reality is often much more complicated. Tsukuba, Japan - An earthquake is generally viewed to be caused by a rupture along a fault that is transmitted outward from its point of origin in a uniform, predictable pattern. The dashed rectangles highlight the rupture events recognised by this study. Lower-right panel shows the spatiotemporal distribution of the slip migration, projected along the north-south direction. Blue lines are our estimate of the faults, along with the fault movements indicated as arrows. Lower-left panel show the enlarged map of our result. Upper panels summarise the regional map of the study area, showing plate boundary (dashed line), seafloor fracture zones (solid lines), the epicentre (star) of the 2018 Gulf of Alaska earthquake and the aftershocks (dots). ![]()
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