![]() Future work can refine our understanding of FGF age and evolution. ![]() We conclude that FGFs show promise for investigating both past earthquake shaking and its spatial variability along the coasts of Oregon and Washington, where sea stacks are often prevalent. Earthquakes cost the nation an estimated 14.7 billion annually in building damage and associated losses according to a new report released jointly today by the U.S. Results for inland features, such as speleothems, are in close agreement with the predictions. FGFs with the lowest breaking accelerations are distributed uniformly over 130 km of coastline. Among the sea stacks old enough to have survived multiple megathrust earthquakes ( n = 16), eight yield breaking accelerations lower than the predictions, although they generally overlap within uncertainty. Among the surveyed FGFs, sea stacks have particular advantages for use as ground. We documented 58 features with fragile geometric characteristics, as determined from field measurements of size and strength, historical photographs, and light detection and ranging point clouds. ![]() We provide context for the quasi‐static results by comparing them with predictions from kinematic simulations and ground‐motion prediction equations. Here, we describe our field survey of FGFs in southern Oregon. Using a quasi‐static analysis, we estimate the minimum horizontal ground accelerations that could fracture the rock pillars. ![]() About 40% of the surveyed sea stacks appear to have survived multiple Cascadia megathrust earthquakes. Among the surveyed FGFs, sea stacks have particular advantages for use as ground‐motion constraints: (1) they are frequently tall and thin (2) they are widely distributed parallel to the coast, proximal to the trench and the likely megathrust rupture surface and (3) they are formed by sea cliff retreat, meaning that their ages may be coarsely estimated as a function of distance from the coast. Earthquake - Magnitude 4.0 - OFFSHORE BAJA CALIFORNIA, MEXICO - 2023 April 27, 18:46:58 UTC earthquakes today - recent and latest earthquakes, earthquake map and earthquake information. Here, we describe our field survey of FGFs in southern Oregon. These empirical constraints are particularly important in regions such as the Pacific Northwest that have not experienced a megathrust earthquake in written history. MB - Montana Bureau of Mines and Geology. ISMPKANSAS - USGS Induced Seismicity Project (Kansas) LD - Lamont-Doherty Cooperative Seismographic Network. ISCGEMSUP - ISC-GEM Supplementary Catalog. We also analyze the hypothetical alerting performance of ShakeAlert had public alerting been available throughout southern California.Fragile geologic features (FGFs), which are extant on the landscape but vulnerable to earthquake ground shaking, may provide geological constraints on the intensity of prior shaking. GCMT - Lamont-Doherty Earth Observatory Global CMT project, New York, USA. A number of software and hardware issues that were responsible for the magnitude underestimation of the mainshock have been identified and will be addressed in future ShakeAlert releases. For the M w 7.1 event, public alerts for Los Angeles County were warranted, but ShakeAlert underpredicted the shaking levels, because both the point‐source and finite‐fault algorithms underestimated the magnitude of the earthquake by 0.8 units. For the M w 6.4 event, this was accurate. No public alerts were sent out by the ShakeAlertLA cell phone app (the only publicly available alerting method at the time), because the predicted shaking for Los Angeles County was below the app’s alerting threshold of modified Mercalli intensity 4.0. ShakeAlert detected and characterized both the M w 6.4 and M w 7.1 earthquakes within 6.9 s of their origin times and created alert messages that were available to ShakeAlert’s pilot users. 1974-1992: TEIC earthquake bulletin and St Louis Regional Catalog 1993-1994: Saint Louis University and Central Mississippi Valley Earthquake Bulletins. Although the system performed reasonably well overall, the sequence also revealed various issues and short comings that will be addressed in impending and future system upgrades. In this study, we dissect log files and replay data through the system to reconstruct the sequence of events and analyze the performance of the system during that period. ShakeAlert created alert messages for the two largest events and for many of the larger aftershocks. West Coast, was operational during this time, although public alerting was only available within Los Angeles County. Geological Survey (USGS) earthquake early warning system being developed for the U.S. During July 2019, a sequence of earthquakes, including an M w 6.4 foreshock and an M w 7.1 mainshock, occurred near Ridgecrest, California.
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