Update for Jan. 10
The City of Seattle and King County "Great Gun Buyback" event on Jan. 26 will provide $100 to $200 Amazon gift cards to those who anonymously turn in firearms, and police have now detailed what will happen with all those guns:

Sentenced to melt over a 3100 degree Fahrenheit cauldron of fire.

Seattle Police said they will take all guns collected during the event and take them to the Nucor steel plant in West Seattle.

With police present, Nucor workers will take the guns, load them into a large metal scoop, and melt them over the cauldron.

From there, the steel is used to fabricate rebar, a basic building material.

SPD has been working with Nucor for years to destroy firearms recovered by police but no longer needed for investigations or as evidence in court proceedings.

SPD also released details on how to distinguish between a regular gun and an assault weapon (regular guns get $100, assault weapons get $200):

"While the state doesn’t have anything on the books defining “assault weapons”, here’s what our in-house gun experts came up with for the purposes of the gun buyback:

A semiautomatic rifle that has an ability to accept a detachable magazine and has at least 2 of the following:
A folding or telescoping stock
A pistol grip that protrudes beneath the action of the weapon
A bayonet mount
A flash suppressor or threaded barrel designed to accommodate a flash suppressor
A grenade launcher

A semiautomatic pistol that has an ability to accept a detachable magazine and has at least 2 of the following:
An ammunition magazine that attaches to the pistol outside of the pistol grip
A threaded barrel capable of accepting a barrel extender, flash suppressor, forward handgrip, or silencer
A shroud that is attached to, or partially or completely encircles, the barrel and that permits the shooter to hold the firearm with the non-trigger hand without being burned
A manufactured weight of 50 ounces or more when the pistol is unloaded

A semiautomatic shotgun that has at least 2 of the following:
A folding or telescoping stock
A pistol grip that protrudes conspicuously beneath the action of the weapon
A fixed magazine capacity in excess of 5 rounds
An ability to accept a detachable magazine
If you’re unsure whether or not one of your guns is an assault weapon, that’s OK. We’ll have on-site SPD experts at the ready during the buyback to help out. Just remember: be careful, and handle all firearms as if they were loaded."

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Original post on Jan. 8
City and county gun buyback effort aiming to limit violence

$100 for handguns, $200 for assault weapons will be paid at Jan. 26 event

The tragic shootings that have dominated headlines and led to a renewed national debate over gun control have prompted the first area gun buy back program in 20 years. In a partnership effort between the City of Seattle and King County an event, set for January 26 in downtown Seattle, will pay for handguns and assault weapons in hope of reducing gun violence.

Mayor Mike McGinn, King County Executive Dow Constantine, Seattle Police Deputy Chief Nick Metz, Dr. David Fleming of Public Health – Seattle & King County, Renee Hopkins of the Seattle Police Foundation, and Reverend Aaron Williams of Seattle’s Mount Zion Baptist Church made the announcement of the Gun Safety Initiative, which includes the gun buyback program. Former Seattle mayors Greg Nickels, Norm Rice, Charles Royer and Wes Uhlman are serving as co-chairs of the program.

The gun buyback will be held on Saturday, January 26, 2013, from 9:00 am to 3:00 pm, in downtown Seattle in the parking lot underneath Interstate 5 between Cherry and James Streets.

In a press release about the announcement Mayor McGinn said, “This gun buyback program can help us protect public health and safety and reduce gun violence in our communities. We will continue working with the police department and other organizations and agencies on a broad range of solutions to the epidemic of gun violence. I want to thank Amazon, PEMCO, the 5 Point Café and Big Mario’s Pizza, SEOMoz, and other sponsors who are making this program possible.”

“If we can prevent just one child, one innocent bystander, from being the victim of a random accident, or the target of an unstable person, it will be well worth our time and effort,” said King County Executive Dow Constantine.

Chief Metz said, “This is an opportunity for people to get unwanted guns out of their homes. We hope that people will take advantage of this opportunity to safely dispose of those unwanted, unused, and forgotten guns that we know are lying around. If this prevents just one tragedy, it is worth the effort.”

“The Sheriff’s Office remains committed to providing a safe place for citizens to turn in guns they no longer want. It is a much better choice to remove an unwanted gun from your home than to leave it where it can be stolen and used in a crime,” said King County Sheriff John Urquhart.

"The Seattle Police Foundation is proud to partner with the Seattle Police Department and many other community partners to improve the safety of our community by removing unwanted guns, helping ensure wanted guns are safely secured and providing vital gun safety educational information to our community," said Renee Hopkins, executive director of the Seattle Police Foundation.

The initiative will extend well beyond the buyback day on the 26th.

A law enforcement partnership between the Seattle Police Department, other law enforcement agencies in King County, community and faith based organizations, will set up locations throughout Seattle and King County where individuals can turn in firearms anonymously, with no questions asked.

The program is modeled on successful gun buyback programs across the country, and the Seattle/King County gun buyback program will consist of an anonymous process in which individuals can turn in their unwanted weapons. No pictures will be taken of participants, nor will law enforcement be logging license plate numbers or running ballistic tests on the guns that are turned in.

In exchange for dropping off hand guns, shotguns, or rifles individuals will receive a gift card valued at up to $100.00. They will receive a $200.00 gift card in exchange for assault weapons (as classified in the State of Washington).

The Seattle Police Department will also be distributing trigger locks for those who wish to secure their firearms safely. These will be available at each of the five precincts during normal business hours.

The press release explained that the Seattle Police Foundation has committed $25,000 to the Gun Safety Initiative, and will serve as the program coordinator. Corporate sponsors include Amazon, which has committed $30,000 in gift cards that will serve as a monetary incentive for those turning in a gun. PEMCO has contributed $5,000, and SEOmoz, a Seattle-based search engine and social optimization software company, has contributed $10,000, and the 5 Point Café and Big Mario’s Pizza has contributed $500. Their funding, along with that of the Seattle Police Foundation, will go toward the purchase of gift cards from other local vendors besides Amazon. Eli Lilly has contributed $1,500 in advertising. Nucor Steel has agreed to make an in-kind contribution and will melt down the guns turned in. The Seattle Police Foundation will continue to solicit contributions to support the gun buyback effort.

Community partners of the gun buyback effort include the Associated Recreation Council, Café Racer, Mount Zion Baptist Church, and the Seattle Metropolitan Chamber of Commerce.

The Seattle Police Department last held a gun buyback program in 1992. Members of the public interested in donating to support the program can do so online via the Seattle Police Foundation website at http://www.seattlepolicefoundation.org.