Question

differentiate between focus and epicenter.

Answer 1

Hi friend

Epicenter-The point on the Earth's surface located directly above the focus of an earthquake. Focus-The location where the earthquake begins (typically underground).

Answer 2

The focus is the pointunder ground where the earthquake rupture physically starts.The epicentre is the location of the focus on a map. Basically, epicentre + depth = focus.To expand on this, thefocus is only where the earthquake starts,not really the ‘location’ of the earthquake, because an earthquake rupturehas a physical size; and for large earthquakes (magnitude 7+), the focus and epicentre is not always a good indicator of where theworst damage may be because the strongest shaking could potentially be several hundred kilometres from the epicentre/focus, and possibly even on completely different faults.Some examples of this are the September 2010 earthquake in Canterbury, NZ, wherethe epicentre was about 10km north of the main rupture; the April 2015 Nepal earthquake, where therupture moved primarily east of the epicentre, causing severe damage to Kathmandu, while Pokhara was relatively unscathedMatthew Bennett's answer to Why was Pokhara not affected by the earthquake even though epicenter is 77km far almost same as Kathmandu?;and the November 2016 Kaikoura earthquake in NZ, where more than 10 faults ruptured, some of them up to 200km north of the epicentre.Depth is important too. A magnitude 7 with a focus 5km deep will likely rupture to the surface,and could flatten a city, while a magnitude 7with a focus 200km deep is unlikely to do anything more than scare a few people.The reason the epicentre is used is because it is fairly easy to find using the time the first earthquake waves reach seismometers; it is usually a good indicator of where theworst damage will be;and people like to seea dot on a map they can point at.