$re = '/(?<=Location: ).*?(?= ;)/m';
$str = '<description>Origin date/time: Mon, 29 Mar 2021 04:23:32 ; Location: BLACKFORD,PERTH/KINROSS ; Lat/long: 56.284,-3.759 ; Depth: 7 km ; Magnitude: 1.0</description>';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php