Upstart automaker Tesla Motors TSLA +3.05% won’t sell as many cars this year as Chevrolet sells in 3 days, but its early success with the all-electric Model S sedan is already keeping the competition up at night. An examination of sales data from across the U.S. and in California for the first half of 2013 paints a picture of just why that is. While Tesla delivered right around 10,000 cars through two quarters, those sales appear to be coming at the expense of BMW, Mercedes, Lexus and Porsche. And Tesla’s sales are remarkably — though perhaps not surprisingly — concentrated in California thus far, with nearly half winding up in the Golden State. As the automaker continues to open new sales and service locations across the country while simultaneously growing its network of high-speed Supercharger stations, things are likely to get a bit worse for the imports.