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2021 South Sandwich Islands Earthquakes
The 2021 South Sandwich Islands earthquakes were a pair of powerful earthquakes, followed by about a thousand strong aftershocks which struck along the South Sandwich Trench in August 2021. The quakes measured 7.5 and 8.1 on the moment magnitude scale, according to the United States Geological Survey. The mainshock is tied with another event in 1929 as the largest earthquake ever recorded in this region and the Atlantic Ocean as a whole, and is tied with the 2021 Kermadec Islands earthquake as the second largest earthquake of 2021. Tectonic setting These earthquakes occurred in the Scotia subduction zone, where the South American plate subducts westward beneath the Scotia Plate and South Sandwich microplate (a component of the broader Scotia plate) at a rate of 71 mm/yr. Both earthquakes were the result of intraplate reverse faulting within the lithosphere of the subducting South American plate. The 7.5 foreshock was located at a depth of 47 km, placing it wit ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
South Georgia And The South Sandwich Islands
) , anthem = "God Save the King" , song_type = , song = , image_map = South Georgia and the South Sandwich Islands in United Kingdom.svg , map_caption = Location of South Georgia and the South Sandwich Islands in the southern Atlantic Ocean , mapsize = 255px , subdivision_type = Sovereign state , subdivision_name = , established_title2 = Separation from Falkland Islands , established_date2 = 3 October 1985 , official_languages = English , demonym = , capital = King Edward Point , coordinates = , largest_settlement = capital , largest_settlement_type = largest settlement , ethnic_groups = , ethnic_groups_year = , government_type = Directly administered dependency under a constitutional monarchy , leader_title1 = Monarch , leader_name1 = Charles III , leader_title2 = Commissioner , leader_name2 = Alison Blake , national_representation = Government of the United Kingdom , national_representation_type1 = Minister , national_representation1 = Zac Go ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Focal Mechanism
The focal mechanism of an earthquake describes the deformation in the source region that generates the seismic waves. In the case of a fault-related event it refers to the orientation of the fault plane that slipped and the slip vector and is also known as a fault-plane solution. Focal mechanisms are derived from a solution of the moment tensor for the earthquake, which itself is estimated by an analysis of observed seismic waveforms. The focal mechanism can be derived from observing the pattern of "first motions", that is, whether the first arriving P waves break up or down. This method was used before waveforms were recorded and analysed digitally and this method is still used for earthquakes too small for easy moment tensor solution. Focal mechanisms are now mainly derived using semi-automatic analysis of the recorded waveforms. Moment tensor solutions The moment tensor solution is typically displayed graphically using a so-called ''beachball'' diagram. The pattern of en ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
History Of The United States
The history of the lands that became the United States began with the arrival of Settlement of the Americas, the first people in the Americas around 15,000 BC. Native American cultures in the United States, Numerous indigenous cultures formed, and many saw transformations in the 16th century away from more densely populated lifestyles and towards reorganized polities elsewhere. The European colonization of the Americas began in the late 15th century, however most colonies in what would later become the United States were settled after 1600. By the 1760s, the Thirteen Colonies, thirteen British colonies contained 2.5 million people and were established along the East Coast of the United States, Atlantic Coast east of the Appalachian Mountains. After French and Indian Wars, defeating France, the British government imposed a series of taxes, including the Stamp Act 1765, Stamp Act of 1765, rejecting the colonists' constitutional argument that new taxes needed their approval. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
2021 Chignik Earthquake
An earthquake occurred off the coast of the Alaska Peninsula on July 28, 2021, at 10:15 p.m. local time. The large megathrust earthquake had a moment magnitude () of 8.2 according to the United States Geological Survey (USGS). A tsunami warning was issued by the National Oceanic and Atmospheric Administration (NOAA) but later cancelled. The mainshock was followed by a number of aftershocks, including three that were of magnitude 5.9, 6.1 and 6.9 respectively. This was the largest earthquake in the United States since the 1965 Rat Islands earthquake, and the 7th largest earthquake in US history. It was also the strongest earthquake globally since the 2015 Illapel earthquake, tying the 2017 Chiapas earthquake and 2018 Fiji earthquake. No casualties or serious damage were reported in the aftermath of the mainshock, as well as some of the strong aftershocks. In Perryville, the closest populated area to the quake, cracks appeared in drywalls and on the ground. Some homes were als ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Surface-wave Magnitude
The surface wave magnitude (M_s) scale is one of the magnitude scales used in seismology to describe the size of an earthquake. It is based on measurements of Rayleigh surface waves that travel along the uppermost layers of the Earth. This magnitude scale is related to the local magnitude scale proposed by Charles Francis Richter in 1935, with modifications from both Richter and Beno Gutenberg throughout the 1940s and 1950s. It is currently used in People's Republic of China as a national standard (GB 17740-1999) for categorising earthquakes. Recorded magnitudes of earthquakes through the mid 20th century, commonly attributed to Richter, could be either M_s or M_L. Definition The formula to calculate surface wave magnitude is: :M_s = \log_\left(\frac\right)_ + \sigma(\Delta)\,, where A is the maximum particle displacement in surface waves (vector sum of the two horizontal displacements) in μm, T is the corresponding period in s (usually 20 2 seconds), Δ is the epi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Body Wave Magnitude
Body-waves consist of P-waves that are the first to arrive (see seismogram), or S-waves, or reflections of either. Body-waves travel through rock directly. mB scale The original "body-wave magnitude" – mB or mB (uppercase "B") – was developed by and to overcome the distance and magnitude limitations of the scale inherent in the use of surface waves. is based on the P- and S-waves, measured over a longer period, and does not saturate until around M 8. However, it is not sensitive to events smaller than about M 5.5. Use of as originally defined has been largely abandoned, now replaced by the standardized scale. mb scale The mb or mb scale (lowercase "m" and "b") is similar to , but uses only P-waves measured in the first few seconds on a specific model of short-period seismograph. It was introduced in the 1960s with the establishment of the ''World-Wide Standardized Seismograph Network'' (WWSSN); the short period improves detection of smaller events, and better discri ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tsunami Earthquake
In seismology, a tsunami earthquake is an earthquake which triggers a tsunami of significantly greater magnitude, as measured by shorter-period seismic waves. The term was introduced by Japanese seismologist Hiroo Kanamori in 1972. Such events are a result of relatively slow rupture velocities. They are particularly dangerous as a large tsunami may arrive at a coastline with little or no warning. Characteristics The distinguishing feature for a tsunami earthquake is that the release of seismic energy occurs at long periods (low frequencies) relative to typical tsunamigenic earthquakes. Earthquakes of this type do not generally show the peaks of seismic wave activity associated with ordinary events. A tsunami earthquake can be defined as an undersea earthquake for which the surface wave magnitude Ms differs markedly from the moment magnitude Mw, because the former is calculated from surface waves with a period of about 20 seconds, whereas the latter is a measure of the total ene ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hiroo Kanamori
is a Japanese seismologist who has made fundamental contributions to understanding the physics of earthquakes and the tectonic processes that cause them. Career Kanamori and American seismologist Thomas C. Hanks developed the moment magnitude scale which replaced the Richter magnitude scale as a measurement of the relative strength of earthquakes. Kanamori invented the method for calculating slip distribution on the fault plane by teleseismic waveform with Masayuki Kikuchi. In addition, they studied realtime seismology. In 2007 he was awarded the Kyoto Prize in Basic Sciences. Kanamori developed a new method of earthquake early warning detection by rapid analysis of the P-wave by a robust network. The algorithm is currently being tested with the Southern California Seismic Network "ShakeAlert" Earthquake Early Warning (EEW) system, and is one of three algorithms that is used by the system. Honours *1993 Arthur L. Day Prize and Lectureship *1994 Asahi Prize *1996 Walter ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Earthquake Rupture
In seismology, an earthquake rupture is the extent of slip that occurs during an earthquake in the Earth's crust. Earthquakes occur for many reasons that include: landslides, movement of magma in a volcano, the formation of a new fault, or, most commonly of all, a slip on an existing fault. Nucleation A tectonic earthquake begins by an initial rupture at a point on the fault surface, a process known as nucleation. The scale of the nucleation zone is uncertain, with some evidence, such as the rupture dimensions of the smallest earthquakes, suggesting that it is smaller than 100 m while other evidence, such as a slow component revealed by low-frequency spectra of some earthquakes, suggest that it is larger. The possibility that the nucleation involves some sort of preparation process is supported by the observation that about 40% of earthquakes are preceded by foreshocks. However, some large earthquakes, such as the M8.6 1950 India - China earthquake., have no foreshocks and it re ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nanyang Technological University
The Nanyang Technological University (NTU) is a national research university in Singapore. It is the second oldest autonomous university in the country and is considered as one of the most prestigious universities in the world by various international metrics. It is usually ranked amongst the world's top 20 institutions of higher learning. NTU is ranked 19th in the world according to the 2023 QS World University Rankings, and has also been ranked 1st globally amongst young universities by the QS World University Rankings since 2015. The university is organised into several colleges and schools, including the College of Engineering, College of Science, Nanyang Business School, Lee Kong Chian School of Medicine, College of Humanities, Arts and Social Sciences, Graduate College, National Institute of Education, and S. Rajaratnam School of International Studies. NTU is also home to several Research Centres of Excellence such as the Earth Observatory of Singapore and Singapore Cent ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Transform Fault
A transform fault or transform boundary, is a fault along a plate boundary where the motion is predominantly horizontal. It ends abruptly where it connects to another plate boundary, either another transform, a spreading ridge, or a subduction zone. A transform fault is a special case of a ''strike-slip fault'' that also forms a plate boundary. Most such faults are found in oceanic crust, where they accommodate the lateral offset between segments of divergent boundaries, forming a zigzag pattern. This is a result of oblique seafloor spreading where the direction of motion is not perpendicular to the trend of the overall divergent boundary. A smaller number of such faults are found on land, although these are generally better-known, such as the San Andreas Fault and North Anatolian Fault. Nomenclature Transform boundaries are also known as conservative plate boundaries because they involve no addition or loss of lithosphere at the Earth's surface. Background Geophysicist ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
