A number of Scottish moved to the Northern & NE corners of England for the mining, and a lesser extent than the Irish for shipping, industries. It's why around places like Newcastle you've got the Geordie accent & then you've the separate dying out pitmatic dialects (with the rolling Rs of the Scots) of the once close knit mining families/communities. This however likely isn't the issue for you.
Hello Nacht
Regarding Northumbria, I believe these dialects were already long in place possibly hundereds of years before mining, if you mean during the Industrial age etc.
The Northumbrian Dialect is strongly derived from the old Anglian and Scandinavian languages. The Lowland Scots accent is from much the same,and is distinct from the Dominant Gallic/Celtic language area's. It is believed to of originated from the Anglo-Saxon Settlement, (mainly Anglian ) of Northumbria, during the 5th to 9th Centuries. Two Anglo Saxon kingdoms united, to form what became known as Northumbria, one in the North known as 'Bernicia', and one in the South known as 'Deira',reaching as far as the Humber river.
Northumbria had also once stretched much further North, and included much of what is now known as Lowland Scotland,including Edinburgh, and beyond even the Clyde, and this is the root of the 'Scots Anglian/English' dialect, which is very distinct but can be seen to be very close and recognisable by people of the Northumberland and Durham areas etc today.
'Pitmatic' is mostly found further south of the Tyne, in County Durham, and is similarly derived but includes a lot of old Cumbrian/Norse influences, and streches in a band from coast to coast, ie People from the West, ie Lake district, speak virtually the same dialect in the East of County Durham.
Regarding 'Geordie' people still cannot understand how Geordie, today, has so much seemingly strong Scandinavian influence's in their dialects, especially when the area, North of the Tyne etc has very few documented Viking placenames, and settlement names etc.
The Northumbria,area North of the Tyne, ( previously Bernicia )was believed to of remained mostly 'Anglo-Saxon' during the additional Viking/Scandinavian/Invasions and settlements, of the 9th to early 11th century. The area has very few placenames and Settlement evidence from the Viking periods which would be expected, knowing the root of the dialects.
One reason not given much thought, could possibly be due to an influx of large refugee's fleeing area's devastated by the 'Norman Invasions, and the later 'Harrying of the North' after the failed Anglo-Saxon rebelions, which mostly began in Durham 1069, after 700 hundred Normans were believed killed there.
That large numbers fled their traditional homes, to the North, and oversea's, is an accepted view. These large movements of peoples were mostly of Anglo/Scandinavian descent and culture, and were fleeing from the Southern area's of Durham,Yorkshire,and Lincolnshire etc, areas that were previously heavily settled by both mainly Anglian (Anglo-Saxon), and Scandinavian ( Viking ) peoples with cultures and dialects that had been established for nearly 200 years.
People are still trying to locate and find out how these distinct two Northern dialects came to exist and where they came from.
Regarding Living DNA and their results I think Northumbria % needs to be clarified, as 'Northumbria' could also genetically include both, Scotland, and England.
Northumbria previously included, Galloway, Dumfries, Cumbria, Northumberland, Yorkshire, Durham, and even other area's etc which could all be deemed 'Northumbrian'.