Rupture Zones Of Great Earthquakes Research Articles

The long-term earthquake forecast for the Kuril-Kamchatka island arc for the September 2013 to August 2018 period; the seismicity of the arc during preceding deep-focus earthquakes in the sea of Okhotsk (in 2008, 2012, and 2013 at M = 7.7, 7.7, and 8.3)

Work was performed in 2008–2014 on the long-term prediction of great earthquakes at the Kuril-Kamchatka arc based on patterns that are observable in the locations of the rupture zones of great earthquakes (seismic gaps) and in the seismic cycle for such earthquakes. The prediction method has been successfully developed and applied to the region since 1965 (the LTEP method). This paper presents a long-term seismic forecast for the September 2013 to August 2018 period for the Kuril-Kamchatka arc earthquake-generating zone. The forecast predicts the following quantities for 20 constituent segments: phases of the seismic cycle, the normalized rate of small earthquakes A10, the magnitudes of moderate-size earthquakes to be expected with probabilities 0.8, 0.5, and 0.15, the maximum possible magnitudes and probabilities of occurrence for great (M ≥ 7.7) earthquakes in the most active depth interval, viz., 0–80 km. We also discuss the seismic process in this region for the 2008–2013 period, namely, the patterns that are observable in the locations of earthquake swarms, the values of and changes in several characteristics of the seismic process in the Kuril-Kamchatka seismic zone during the period 2008–2013, which occurred in relation with great shallow earthquakes beneath the Sea of Okhotsk (July 5, 2008, MW = 7.7; August 14, 2012, MW = 7.7; May 24, 2013, MW = 8.3, and the giant Tohoku earthquake of March 11, 2011 with MW = 9.0). The results corroborate the high seismic hazard for the area of Petropavlovsk-Kamchatskii and the urgent necessity of continuing and intensifying the ongoing work on seismic retrofitting and seismic safety.

Strong plate coupling along the Nazca–South America convergent margin

The force balance in plate tectonics is fundamentally important but poorly known. Here, we show that two prominent and seemingly unrelated observations—trench-parallel gravity anomalies along the Nazca–South America margin that coincide with the rupture zones of great earthquakes, and a rapid slowdown of Nazca–South America convergence over the past 10 m.y.—provide key insights. Both result from rapid Miocene-Pliocene uplift of the Andes and provide quantitative measures of the magnitude and distribution of plate coupling along the Nazca–South America margin. We compute the plate-tectonic force budget using global models of the faulted lithosphere coupled to high-resolution mantle circulation models and find that Andean-related plate-margin forces are comparable to plate-driving forces from the mantle, and they have sufficient magnitude to account for pronounced bathymetry variations along the trench. Our results suggest that plate coupling, gravity anomalies, and bathymetry variations along a given trench are all controlled by long-term stress variations in the upper portion of plate boundaries and that an explicit budget of driving and resisting forces in plate tectonics can be obtained. For the convergent margin considered here, spatial variations in the effective coefficient of friction associated with the distribution of lubricating sediments entering the trench are, by comparison, of minor importance.

Izu detachment hypothesis: A proposal of a unified cause for the Miyake-Kozu event and the Tokai slow event

Abstract Based on the fact that interseismic deformation of collision zones is generally described by slip along a detachment at depth, I attempt to interpret the deformation of the Izu collision zone in terms of a detachment model. The systematic deviation of the GPS velocities of the Izu Peninsula (Nov. 1998–June 2000) from the Philippine Sea-Eurasian relative plate motions is fitted by the slip on the detachment at a depth of 15–20 km with a rate of 3 cm/yr. On June 26, 2000, seismo-magmatic activity that started near Miyakejima expanded NW by 20 km close to Kozushima in association with dike intrusion over a few months. The horizontal movements associated with this event, however, spread over wide areas in central Honshu. Simple dike intrusion models cannot explain these movements. To explain these, I hypothesize that a 20 cm of rapid slip occurred on the detachment at the time of this event. The abnormal crustal movements in the Tokai-central Honshu-Kanto region then started after the event. I propose that they represent delayed diffusive transfer of the slip on the detachment over surrounding low viscosity layers, such as nearby rupture zones of great earthquakes.

Body wave and surface wave analysis of large and great earthquakes along the Eastern Aleutian Arc, 1923–1993: Implications for future events

The 500‐km‐long Alaska Peninsula and Shumagin Islands segments of the Aleutian arc have a moderate to high probability of rupturing in one or more large or great earthquakes in the next few decades. To understand the likely modes of rupture in the next sequence of large and great events and to delineate the current geometry of the plate interface, we determine focal mechanisms, depths, and source time functions from seismic records for the largest events since 1917: the great earthquake of November 10,1938, and seven events with surface wave magnitude (Ms) of 6.9 to 7.5. Teleseismic body waves and surface waves are used to estimate the seismic moment and gross rupture characteristics of the great earthquake of November 10,1938, along the Alaska Peninsula. Body wave inversion of five P and four SH waves gives a duration of about 110 s in which moment was released in two episodes, each of about 50 s duration, with the second being larger than the first. The first source was located in the general vicinity of the epicenter of the mainshock, and the second, which occurred about 60 s later, was centered about 180 km to the northeast. The body‐wave‐derived seismic moment is 3.7×1021 N m (Mw 8.3). We corroborate the body wave results by calculating surface waves by normal‐mode summation and comparing them with data at periods greater than 50 s. An adequate fit to observed seismograms is obtained for either a single point source or two point sources, with one located about 180 km northeast of the mainshock epicenter. Rupture in 1938 appears to have been confined to the Alaska Peninsula segment; uniform rupture into the Shumagin region is not supported by the data. The Ms 6.9 earthquake of May 13,1993, ruptured a small portion of the Shumagin gap. The earthquake of May 14,1948, (Ms 7.5) occurred on a shallow dipping thrust fault with a depth of about 31 km, not 60 km as originally suggested. Five Ms ∼ 7 events in the 1938 rupture zone have locations, depths, and mechanisms that define a shallow dipping (16°–19°) plate interface which shallows to 8° under Kodiak Island. Subduction of seamounts of the Gulf of Alaska seamount province may explain the location, moment, focal mechanism, and depth of the five Ms ∼ 7 events. The plate interface dips nearly uniformly between the Alaska Peninsula and Shumagin segments, indicating that segmentation, if any, is not controlled by the orientation of the plate interface. A slight warp of the plate interface may form the boundary between rupture zones of great earthquakes along the Kodiak and Alaska Peninsula segments of the arc and may explain why rupture zones of large to great earthquakes rarely cross this tectonic boundary.

Comparison of seismicity parameters in different subduction zones and its implications for the Cascadia Subduction Zone

The Cascadia subduction zone is a young subduction zone with associated volcanic activity but with no history of large thrust earthquakes associated with it as is characteristic of other subduction zones. This has led to questions about the potential for great earthquakes associated with this subduction. The seismic potential associated with this subduction has been investigated in this study by examining and comparing the number of shallow earthquakes with magnitude >6 which have occurred in different subduction zones since 1910. This examination shows that all subduction zones exhibit a higher level of activity than Cascadia. Furthermore, two of these zones with similar rates of plate motion and age at subduction, the Rivera plate and southwest Japan, have not only experienced great earthquakes but show a higher rate of activity than the Cascadia zone. The activity rate in subduction zones with predominantly aseismic slip is also higher than the activity rate in the Cascadia zone. Earthquake activity in the rupture zones of great earthquakes both before and after the occurrence of great earthquakes is higher than the activity rate in the Cascadia zone. These results therefore suggest that the low rate of activity in the Cascadia zone is unusual and supports the idea that the subduction here is different and that perhaps the potential for great earthquakes cannot be extrapolated simply on the basis of certain similarities between the Cascadia zone and other subduction zones with a history of great earthquakes. The low rate of earthquake activity in the Cascadia zone can, however, be explained on the basis of the combined effect of low rate of plate motion, significant aseismic subduction, and young age at subduction. The activity rate in the Cascadia zone is consistent with the activity rates in other subduction zones if it is assumed that much of the plate motion is accommodated aseismically. The seismic slip rate associated with this subduction zone is a small fraction of the rate of plate motion, and therefore even if the potential for great earthquakes may exist, the return period for great earthquakes will be much longer (2 or 3 times) than in other zones with similar characteristics such as the Rivera plate or southwest Japan.

Rupture zones of great earthquakes in the Himalayan region

The four major earthquakes that have occurred in the Himalayan region since 1897 seem to have ruptured as little as about 15% or 20% to perhaps as much as 45% of the thrust zone separating the underthrusting Indian Shield and the overthrusting Himalayan crystalline nappes. Because of various difficulties in estimating the rupture zones for each of these earthquakes, we cannot place a tight constraint on the fraction of the Himalayan belt for which the risk of an imminent great earthquake is high. If a slip between the Indian Shield and the Himalayan crystalline nappes occurs largely by slip associated with major earthquakes, then recurrence intervals of such earthquakes are likely to be between 200 and 500 years, with a likely value of 300 years.

Rupture Zones of Great Earthquakes in the Alaska-Aleutian Arc, 1784 to 1980

Historical documents indicate that great earthquakes ruptured at least a 500-kilometer-long segment of the plate boundary near the Alaska Peninsula in 1788 and 1847. At least half of a major seismic gap in the Shumagin Islands ruptured during those shocks but has not experienced a great earthquake for at least 77 years. Large shocks along this and other plate boundaries occur in bursts followed by several decades during which there is very little energy release.