Magnitude 6.5 Earthquake in Nye County, Nevada.

The United States Geological Survey recorded a Magnitude 6.5 Earthquake at a depth of 2.8 km, roughly 56 km to the west of the town of Tonopah in Nye County, Nevada, slightly after 4.00 pam local time (slightly after 11.00 am GMT) on Friday 15 May 2020. There are no reports of any casualties or damage to buildings associated with this quake, but a number of roads have been closed due to fracturing. This is the largest recorded Earthquake in Nevada since 1954, and people have reported feeling it across Nevada, California, Oregon, Arizona and Utah, as well as in parts of Washington, Idaho, Wyoming, and Colorado states in the US, as well as Baja California in Mexico.

Damage to the US 95 highway in Esmeralda County, Nevada, following the state's largest Earthquake in 66 years, on Friday 15 May 2020. Esmeralda County Sheriff's Office.

Nevada is a zone of active mountain orogeny (mountain growth), fuelled by the subduction zone on the American West Coast. The state is criss-crossed by faults associated with its many growing mountain ranges. The rocks of the North American lithosphere are being pushed to the east by seafloor spreading beneath the Pacific and to the west by seafloor spreading beneath the Atlantic. This results in folding and upthrust within the plate, principally in the Rocky Mountains, which run along the western margin of the North American Plate, close to the subduction and fault zones of the continent's west coast. This folding and thrusting leads to frequent Earthquakes throughout the Rocky Mountain and areas to the west.

 The approximate location of the 15 May 2020 Nye County Earthquake swarm. USGS.

Earthquakes are considered to cause as mucg Earth movement in Nevada as they do in neighbouring California, however, while California suffers a large number of relatively small Earthquakes, the interval between Earthquakes in Nevada tends to be longer, with the effect that pressure on the state's thirty plus major faults tends to build up much more between events, and subsequently Earthquakes tend to be much larger.

Witness accounts of Earthquakes can help geologists to understand these events and the underlying structures that cause them. If you felt this quake (or if you were in the area but did not, which is also useful information) then you can report it to the United States Geological Survey here.

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Rosagammarus minichiellus: Not an Amphipod after all?

Amphipods are small Crustaceans found in almost all modern marine ecosystems, as well as many freshwater environments; most freshwater 'Shrimps' are Amphipods, as are the semi-terrestrial Sandhoppers. The group have a fossil record that dates back to the Eocene, with specimens known from Baltic Amber. In September 2013 Mark McMenamin, Lesly Zapata, and Meghan Hussey of the Department of Geology and Geography at Mount Holyoke College, published a paper in the Journal of Crustacean Biology describing Rosagammarus minichiellus, a putative Amphipod from the Late Triassic Shaly Limestone Member of the Luning Formation of Nye County in Nevada. This extended the fossil record of the group back about 150 million years, which is extraordinary, although since the group is predicted to have had a Carboniferous origin, not totally unreasonable. However they further suggested the specimen might be a member of the Acanthogammaridae, a group with no previous fossil record currently restricted to Lake Baikal in Russia, and generally assumed to be a highly derived group that evolved in that habitat.

Rosagammarus minichiellus, Luning Formation, Nevada, Triassic. (A) Photograph of fossil specimen; scale bar in centimeters; (B) diagrammatic sketch identifying key parts of exoskeleton. Abbreviations are as follows: B, basis; c, carpus; cx, coxa; CP, coxal plate; G, gnathopod; i, ischium; m, merus; Pp, pereiopod; Pt, pereionite; S, spine. McMenamin et al. (2013).

The specimen from which the species was described is fragmentary, comprising a partial Arthropod exoskeleton which McMenamin et al. interpreted as several partial limbs and part of the trunk of an Amphipod Crustacean.

Rosagammarus minichiellus. Reconstruction of entire Amphipod, using a sketch of a generalized Acanthogammarid as template. Fossil material recovered is shown in gray. Head and tail regions are conjectural. Estimated total length 17 cm. McMenamin et al. (2013).

In a second paper, also published in the Journal of Crustacean Biology, on 23 June 2016, Hunter Starr and Thomas Hegna of the Department of Geology at Western Illinois University, and Mark McMenamin of the Department of Geology and Geography at Mount Holyoke College (again) present an alternative interpretation of Rosagammarus minichiellus, which suggests it is not, after all, an Amphipod.

Starr et al. re-examined the Rosagammarus minichiellus specimen, and concluded that the 'limbs' of the specimen were not in fact free, but rather were joined by a flattened plate, holding them fixed in position.

Rosagammarus minichiellus. (A) Specimen photographed with polarized light, and, (B) whitened with ammonium chloride under plain light; (C) interpretive drawing from McMenamin et al. (2013), and (D) new interpretive drawing. Starr et al. (2016).

This interpretation of the fossil is incompatible with it being the limbs of an Amphipod (which need to be free in order for the animal to move). Instead they suggest the specimen may by part of the telsion (tail) of a large, Lobster-like Decapod Crustacean. Decapods have been around since at least the Devonian, and several have been described from the Luning Formation, so this explanation is not problematic. Decapods have a flattened tail with elements connected by a flattened plates, the coxal plates, which gives the Crustacean thrust when swimming. Decapods are also noted for reaching large sizes, so the exceptionally large Amphipod of the original interpretation becomes part of the tail of a more normally sized Decapod.

(M) Photograph showing the location of each elemental map; (N) digital reconstruction of the telson of Rosagammarus minichiellus made by flipping an image of the fossil in photoshop and digitally combining the images; (O) interpretive drawing by McMenamin et al. (2013) with the approximate location of each elemental map indicated. Starr et al. (2016).

See also...

Decapod Crustaceans from the Tarioba Shell Mound.                                                       Shell mounds are archaeological sites common in coastal areas around the world. In Brazil there are hundreds of such mounds, mostly dating to between 8000 and 1000 years ago, with the greatest abundance being found in Espírito Santo and Santa...

A new species of Icriocarcinid Crab from the End Cretaceous of California.                  Icriocarcinid Crabs are a distinct group of...

A new species of Ostracod from the Pleistocene of Sicily.                             Ostracods are small Crustaceans with a bivalved body plan; their body is sandwiched laterally between two large valves, with the animal using its legs...

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