It is the tip of what could prove to be a very large financial fraud iceberg. Jackson County prosecutors and federal officials said Thursday that they have filed criminal charges in a fraud scheme involving the government-sponsored reverse mortgage program — only the second such case filed nationally. But they warned that criminals are looking for ways to cash in as the reverse mortgage program gains popularity. “It’s more of an emerging trend,” said Michael Powell of the US Department of Housing and Urban Development’s office of inspector general. “We’re starting to see it as a bigger problem.”