1) This is why the area immediately inside the entrance of a supermarket is known as the ‘decompression zone’.
Yes: "known" is an adjective here. Verbal "known" is a past participle used in the perfect tense ("I have known him for 10 years"), and in passives with infinitivals ("Max was known to be an alcoholic").
2) Supermarkets do not expect to sell much here, so it tends to be used more for promotion.
No, "used" is not an adjective, but a past participle verb used here with "be" to form the passive voice. Adjectival "used" is found in noun phrases, such as "Kim bought a used car", and in adjectival passives like "Ed isn't used to hard work".