Andrew Nevins on "[Theme: Twenty Thirteen] Remove the responsive version"

The easiest thing you can do is add a min-width to the containing element in your Custom CSS plugin or Child Theme style.css file.
E.g,

#page {
 min-width: 1200px;
}

Use a browser developer tool like the one built-in to Google Chrome to find out all other styles you need to override: http://developers.google.com/chrome-developer-tools/