The most common and most likely answer to this crossword clue is the 9 letter word EPICENTRE
I've seen this crossword clue in Independent
E
P
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C
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E
More clues leading to the result EPICENTRE
- Grand hospital department needing engineers in situation where things fall apart
- Point in shock, impressive food course having no end
- Large-scale course briefly a focus for seismologist
- Story early course is cut short leads to quaking heart?
- Record in Crete possibly a focal point
- It’s bang in the middle of classic course, unfinished
- Marker of collapsed crust?
- Focus of ground-breaking classic course, abridged
- Disaster area on grand scale – go in but there’s a final twist
- Focus of activity in great course, incomplete
Buddy explains!

The straight part
We know that "Marker" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case marker = epicentre.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does EPICENTRE mean?
EPICENTRE noun- The point on the land or water surface directly above the focus, or hypocentre, of an earthquake.
- The point on the surface of the earth directly above an underground explosion.
- The focal point of any activity, especially if dangerous or destructive.
- The geographical area in which an ongoing disaster, illness, crisis, or other destructive event is currently most severe.
- Of an earthquake: to have its epicentre (at a specified location).