Question: What was the length of the fault rupture in the earthquake for which Kenji Satake worked with other scientists to pinpoint a date, time, and location for?
Context: The 1700 Cascadia earthquake occurred along the Cascadia subduction zone on January 26 with an estimated moment magnitude of 8.7–9.2.  The megathrust earthquake involved the Juan de Fuca Plate that underlies the Pacific Ocean, from mid-Vancouver Island in British Columbia, Canada, south along the Pacific Northwest coast as far as northern California.  The length of the fault rupture was about 1000 km with an average slip of 20 m . The 1980 El Asnam earthquake occurred on October 10 at with a moment magnitude of 7.1 and a maximum Mercalli intensity of X ("Extreme").  The shock occurred in the Algerian town of El Asnam (now known as Chlef).  The shocks were felt over 550 km away, with the initial earthquake lasting 35 seconds.  It was the largest earthquake in Algeria, and was followed three hours later by a magnitude 6.2 aftershock.  The earthquake created about 42 km of surface rupture and had a vertical slip of up to 4.2 m .  No foreshocks were recorded.  The earthquake was found to have occurred very close to the epicenter of the 1954 earthquake using joint epicenter determination techniques.  It occurred at a previously unknown reverse fault. The 1931 Fuyun earthquake (富蕴地震) occurred on August 10 at 21:18 UTC.  The epicenter was near Fuyun County of northern Xinjiang, China.  It was a M 8.0 earthquake and had a surface rupture of 171 km with a maximal horizontal displacement of 14 m along the Koktokay-Ertai fault zone (可可托海-二台断裂带).  The Koktokay-Ertai fault has a slip rate of 4±2 mm per year.  The rupture of this earthquake was caused by right-lateral strike-slip movement with normal component.  The rupture is well preserved and becomes one of the main features of the Koktokay National Geopark (可可托海国家地质公园) located in Koktokay. Kenji Satake is a Japanese seismologist who has made significant contributions to subduction and tsunami research.  Along with Brian Atwater and David Yamaguchi, Satake assembled disparate pieces of information regarding a Japanese tsunami that had no known origin.  The three scientists worked together to pinpoint a date, time, and location for the 1700 Cascadia earthquake – 9 p.m on January 26, 1700 – on the Cascadia Subduction Zone off the Pacific Northwest coast of North America. Situated at the boundary to the San Gabriel Valley and San Fernando Valley, the Sierra Madre Fault Zone (also known as the Sierra Madre-Cucamonga Fault) runs along the southern edge of the San Gabriel Mountains for a total of 95 km , where the northwesternmost 19 km comprises the San Fernando Fault (the section responsible for the 1971 San Fernando earthquake).  A 1980s paleoseismic study that included a trench investigation and mapping revealed that a major earthquake had most likely not occurred to the east of the San Fernando rupture area for at least the last several thousand, and possibly the last 11,000 years. The 1838 San Andreas earthquake is believed to be a rupture along the northern part of the San Andreas Fault in June 1838.  It affected approximately 100 km (62 miles) of the fault, from the San Francisco Peninsula to the Santa Cruz Mountains.  It was a strong earthquake, with an estimated moment magnitude of 6.8 to 7.2, making it one of the largest known earthquakes in California.  The region was lightly populated at the time, although structural damage was reported in San Francisco, Oakland, and Monterey.  It is unknown whether there were fatalities.  Based on geological sampling, the fault created approximately 1.5 meters (5.0 feet) of slip. One of the many common features of the Earth's internal and external systems is the process of earthquake ruptures.  Generally, an earthquake rupture refers to a slip, whether on the surface or beneath, in the Earth's crust that results in a fault and displacement of some sort.  Earthquake ruptures occur for many reasons that include: landslides, an eruption of a volcano, the formation of a new fault, or a slip on an existing fault. The 1940 El Centro earthquake (or 1940 Imperial Valley earthquake) occurred at 21:35 Pacific Standard Time on May 18 (05:35 UTC on May 19) in the Imperial Valley in southeastern Southern California near the international border of the United States and Mexico.  It had a moment magnitude of 6.9 and a maximum perceived intensity of X ("Extreme") on the Mercalli intensity scale.  It was the first major earthquake to be recorded by a strong-motion seismograph located next to a fault rupture.  The earthquake was characterized as a typical moderate-sized destructive event with a complex energy release signature.  It was the strongest recorded earthquake to hit the Imperial Valley, and caused widespread damage to irrigation systems and led to the deaths of nine people. The Qayen earthquake, also known as the Ardekul or Qaen earthquake, struck Northern Iran's Khorasan Province on May 10, 1997 at 07:57 UTC (12:57 local time).  The largest in the area since 1990, the earthquake measured 7.3 on the moment magnitude scale and was centered approximately 270 km south of Mashhad on the village of Ardekul.  The third earthquake that year to cause severe damage, it devastated the Birjand–Qayen region, killing 1,567 and injuring more than 2,300.  The earthquake—which left 50,000 homeless and damaged or destroyed over 15,000 homes—was described as the deadliest of 1997 by the United States Geological Survey.  Some 155 aftershocks caused further destruction and drove away survivors.  The earthquake was later discovered to have been caused by a rupture along a fault that runs underneath the Iran–Afghanistan border. Seismologists usually define strong ground motion as the strong earthquake shaking that occurs close to (less than about 50 km from) a causative fault.  The strength of the shaking involved in strong ground motion usually overwhelms a seismometer, forcing the use of accelerographs (or strong ground motion accelerometers) for recording.  The science of strong ground motion also deals with the variations of fault rupture, both in total displacement, energy released, and rupture velocity.
Answer: about 1000 km