This is a question I have had for some time too. For example, I have been in 6.0 quakes that I almost didn't feel at all but also have been in 4.5 to 6.0 quakes that felt like I had been in an explosion when "Land waves" where the land rising up and coming towards you hits buildings and sounds like an explosion often. But, I have only seen a 3 foot high land wave move towards me once in Malibu Canyon in the 1970s. So, I have questions about all this too but my scariest earthquake was no question the 7.1 San Fernando Quake in February 1971.
The 1971 San Fernando earthquake, also known as Sylmar earthquake, struck the San Fernando Valley near Sylmar at 6:00:55 a.m. PST on February 9, 1971, with a magnitude of 6.6.Feb 8, 2016
Earthquakes
are more intense the faster the planet’s crust slams together, which
explains why the shaking causes so much damage in some of the most
populated areas around mountain chains.
Scientists were trying to
understand why some tremors are more intense than others. They used
models of tectonic plates and their movement to make their findings and
found that, according to their paper in the journal Earth and Planetary Science Letters,
the speed at which those plates were crashing into one another was
directly linked to how frequent and how powerful the resulting
earthquakes were.
One reason for this connection is that when two
plates come together quickly, the area over which an earthquake occurs
is larger. Other factors play a role as well, such as the geological
history of the place, the stress on the plates, and temperature.
According to the study, fast-moving plates lead to cooler temperatures
and make the crust more “brittle,” which allows it to release more of
the energy it has built up. Earthquakes are more destructive when tectonic plates smash together faster.Photo: CC0 Creative Commons
“The
impact of large earthquakes in mountain belts is devastating,” lead
study author Luca Dal Zilio, from Swiss university ETH Zürich, said in a
statement from journal publisher Elsevier.
“Our scientific contribution can help the society to develop a more
complete view of earthquake hazard in one of the most densely populated
seismic zones of the world and ultimately take action accordingly.”
The
models the team used in their investigation mimicked the conditions at
four different mountain ranges in Europe and Asia: the Himalayas, which
are home to Mount Everest; the Alps, the biggest mountain chain in
Europe; the Zagros, which are mostly in Iran; and the Apennines in
Italy. In those mountain ranges, smaller tectonic plates — separate from
the seven major plates on Earth that people tend to be familiar with —
rub together to create the quakes that are hazardous to the dense human
settlements around them. Where the plate collisions are slower, there is
less danger associated with the seismic activity.
Mountains themselves can rise up from the ground due to movement in the Earth’s crust and mantle with tectonic plates colliding. Earthquakes are more destructive when tectonic plates smash together faster.Photo: CC0 Creative Commons
Earthquakes are more destructive when tectonic plates smash together faster. Photo: CC0 Creative Commons 
Earthquakes are more destructive when tectonic plates smash together faster. Photo: CC0 Creative Commons 
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