Question: What is the name of the American seismologist and physicist who collaborated with Beno Gutenberg when developing the Richter magnitude scale?

Context articles: Beno Gutenberg
2009 L'Aquila earthquake
Gutenberg Glacier
1931 Dogger Bank earthquake
List of earthquakes in Japan
Charles Francis Richter
Seismicity
Absolute magnitude
Mount Richter
Richter magnitude scale

Beno Gutenberg (June 4, 1889 – January 25, 1960) was a German-American seismologist who made several important contributions to the science.
 He was a colleague and mentor of Charles Francis Richter at the California Institute of Technology and Richter's collaborator in developing the Richter magnitude scale for measuring an earthquake's magnitude.
The 2009 L'Aquila earthquake occurred in the region of Abruzzo, in central Italy.
 The main shock occurred at 03:32 CEST (01:32 UTC) on 6 April 2009, and was rated 5.8 or 5.9 on the Richter magnitude scale and 6.3 on the moment magnitude scale; its epicentre was near L'Aquila, the capital of Abruzzo, which together with surrounding villages suffered most damage.
 There have been several thousand foreshocks and aftershocks since December 2008, more than thirty of which had a Richter magnitude greater than 3.5.
Gutenberg Glacier ( ) is a glacier 8 nmi long in the northern Holyoake Range of the Churchill Mountains of Antarctica.
 It flows northwest between Mount Hubble and Mount Richter to enter Starshot Glacier.
 The glacier was named by the Advisory Committee on Antarctic Names after German-born seismologist Beno Gutenberg, director of the California Institute of Technology seismology laboratory in the 1930s, and collaborator with Charles F. Richter in developing the Richter Scale, 1935, used to measure the magnitude of earthquakes.
The Dogger Bank earthquake of 1931 was the strongest earthquake recorded in the United Kingdom since measurements began.
 It had a magnitude of 6.1 on the Richter magnitude scale, and it caused a shaking intensity of III ("Weak") to IV ("Light") on the Mercalli intensity scale.
 The location of the earthquake in the North Sea meant that damage was significantly less than it would have been had the epicentre been on the British mainland.
This is a list of earthquakes in Japan with either a magnitude greater than or equal to 7.0 or which caused significant damage or casualties.
 As indicated below, magnitude is measured on the Richter magnitude scale ("M") or the moment magnitude scale ("M"), or the surface wave magnitude scale ("M") for very old earthquakes.
 The present list is not exhaustive, and reliable and precise magnitude data is scarce for earthquakes that occurred prior to the development of modern measuring instruments.
Charles Francis Richter ( ); April 26, 1900 – September 30, 1985) was an American seismologist and physicist.
Seismicity is a measure which encompasses earthquake occurrences, mechanisms, and magnitude at a given geographical location.
 As such it summarizes a region's seismic activity.
 The term was coined by Beno Gutenberg and Charles Francis Richter in 1941.
 Seismicity is studied by geophysicists.
Absolute magnitude is a measure of the luminosity of a celestial object, on a logarithmic astronomical magnitude scale.
 An object's absolute magnitude is defined to be equal to the apparent magnitude that the object would have if were viewed from a distance of exactly 10 parsecs (32.6 light years), with no extinction (or dimming) of its light due to absorption by interstellar dust particles.
 By hypothetically placing all objects at a standard reference distance from the observer, their luminosities can be directly compared on a magnitude scale.
 As with all astronomical magnitudes, the absolute magnitude can be specified for different wavelength ranges corresponding to specified filter bands or passbands; for stars a commonly quoted absolute magnitude is the absolute visual magnitude, which uses the visual (V) band of the spectrum (in the UBV photometric system).
 Absolute magnitudes are denoted by a capital M, with a subscript representing the filter band used for measurement, such as M for absolute magnitude in the V band.
Mount Richter ( ) is a mountain rising to 2550 m between Gutenberg Glacier and upper Starshot Glacier in north Holyoake Range, Churchill Mountains.
 The mountain is 3 nautical miles (6 km) north of Mount Hubble.
 Named by Advisory Committee on Antarctic Names (US-ACAN) after Charles F. Richter, American physicist, California Institute of Technology, 1930–70; in collaboration with Beno Gutenberg, 1935, he developed the Richter Scale which bears his name, used to measure the magnitude of earthquakes.
The Richter magnitude scale ("M", also Richter scale) assigns a magnitude number to quantify the size of an earthquake.
 The Richter scale, developed in the 1930s, is a base-10 logarithmic scale, which defines magnitude as the logarithm of the ratio of the amplitude of the seismic waves to an arbitrary, minor amplitude, as recorded on a standardized seismograph at a standard distance.