http://nomisma.org/kml/thasos-all.kml is a KML file that shows findspots of hoards with coins of Thasos in them. You can see that file rendered with the Google Map API at http://nomisma.org/id/thasos.
This post is about viewing the KML file in Google Earth. If you do that, you'll see a Timeline slider appear in the top left of the G Earth window. Slide the control to the right and you'll see an explosion of hoards towards the north following the mid-2nd century BC. It's really quite dramatic so give it a shot.
One part of an explanation is that Thasos started striking large numbers of new larger tetradrachms following 148 BC, with many of these traveling north. Exactly why is a matter of historical interpretation. The Roman province of Macedon was established in 146 B.C. and that had a profound effect on both the issuance and circulation of coinage.
Nomisma.org is about making this information more accessible so that more scholars can engage with the question.