United States Geological Survey in the context of "Saline water"

Topography is the study of forms and features of land surfaces. The topography of an area may refer to landforms and features themselves, or a description or depiction in maps.

Topography is a field of geoscience and planetary science, and is concerned with local detail in general, including not only relief, but also natural, artificial, and cultural features such as roads, land boundaries, and buildings. In the United States, topography often means specifically relief, even though the USGS topographic maps record not just elevation contours, but also roads, populated places, structures, land boundaries, and so on.

An earthquake occurred in the province of Sichuan, China at 14:28:01 China Standard Time on May 12, 2008. Measuring at 8.0 M_s (7.9–8.3 M_w), the earthquake's epicenter was located 80 kilometres (50 mi) west-northwest of Chengdu, the provincial capital, with a focal depth of 19 km (12 mi). The earthquake ruptured the fault for over 240 km (150 mi), with surface displacements of several meters. The earthquake was also felt as far away as Beijing and Shanghai—1,500 and 1,700 km (930 and 1,060 mi) away, respectively—where office buildings swayed with the tremor, as well as Bangkok, Thailand and Hanoi, Vietnam. Strong aftershocks, some exceeding 6 M_s, continued to hit the area up to several months after the main shock, causing further casualties and damage. The earthquake also caused the largest number of geohazards ever recorded, including about 200,000 landslides and more than 800 quake lakes distributed over an area of 110,000 km (42,000 sq mi).

Over 69,000 people lost their lives in the quake, including 68,636 in Sichuan province. 374,176 were reported injured, with 18,222 listed as missing as of July 2008. The geohazards triggered by the earthquake are thought to be responsible for at least one third of the death toll. The earthquake left at least 4.8 million people homeless, though the number could be as high as 11 million. Approximately 15 million people lived in the affected area. It was the deadliest earthquake to hit China since the 1976 Tangshan earthquake, which killed at least 242,000 people, and the strongest in the country since the 1950 Assam–Tibet earthquake, which registered at 8.6 M_w. It was the 4th deadliest natural disaster of the decade. It is the 18th deadliest earthquake of all time. The economic loss of the earthquake was 845.1 billion yuan (US$130 billion). On November 6, 2008, the central government announced that it would spend 1 trillion yuan (about US$146.5 billion) over the next three years to rebuild areas ravaged by the earthquake, as part of the Chinese economic stimulus program.

The volcanic explosivity index (VEI) is a scale used to measure the size of explosive volcanic eruptions. It was devised by Christopher G. Newhall of the United States Geological Survey and Stephen Self in 1982.

Volume of products, eruption cloud height, and qualitative observations (using terms ranging from "gentle" to "mega-colossal") are used to determine the explosivity value. The scale is open-ended with the largest eruptions in history given a magnitude of 8. A value of 0 is given for non-explosive eruptions, defined as less than 10,000 m (350,000 cu ft) of tephra ejected; and 8 representing a supervolcanic eruption that can eject 1.0×10 m (240 cubic miles) of tephra and have a cloud column height of over 20 km (66,000 ft). The scale is logarithmic, with each interval on the scale representing a tenfold increase in observed ejecta criteria, with the exception of between VEI-0, VEI-1 and VEI-2.

Igneous rock (igneous from Latin igneus 'fiery'), or magmatic rock, is one of the three main rock types, the others being sedimentary and metamorphic. Igneous rocks are formed through the cooling and solidification of magma or lava.

The magma can be derived from partial melts of existing rocks in a terrestrial planet's mantle or crust. Typically, the melting is caused by one or more of three processes: an increase in temperature, a decrease in pressure, or a change in composition. Solidification into rock occurs either below the surface as intrusive rocks or on the surface as extrusive rocks. Igneous rock may form with crystallization to form granular, crystalline rocks, or without crystallization to form natural glasses.

Physiographic regions are a means of defining Earth's landforms into independently distinct, mutually exclusive areas, independent of political boundaries. It is based upon the classic three-tiered approach by Nevin M. Fenneman in 1916, that separates landforms into physiographic divisions, physiographic provinces, and physiographic sections.

The classification mechanism has become a popular geographical tool in the United States, indicated by the publication of a USGS shapefile that maps the regions of the original work and the National Park Services's use of the terminology to describe the regions in which its parks are located.

The moment magnitude scale (MMS; denoted explicitly with M_w  or Mwg and generally implied with use of a single M for magnitude) is a measure of an earthquake's magnitude ("size" or strength) based on its seismic moment. M_w  was defined in a 1979 paper by Thomas C. Hanks and Hiroo Kanamori. Similar to the local magnitude/Richter scale (M_L ) defined by Charles Francis Richter in 1935, it uses a logarithmic scale; small earthquakes have approximately the same magnitudes on both scales. Despite the difference, news media often use the term "Richter scale" when referring to the moment magnitude scale.

Moment magnitude (M_w ) is considered the authoritative magnitude scale for ranking earthquakes by size. It is more directly related to the energy of an earthquake than other scales, and does not saturate – that is, it does not underestimate magnitudes as other scales do in certain conditions. It has become the standard scale used by seismological authorities like the United States Geological Survey for reporting large earthquakes (typically M > 4), replacing the local magnitude (M_L ) and surface-wave magnitude (M_s ) scales. Subtypes of the moment magnitude scale (M_ww , etc.) reflect different ways of estimating the seismic moment.