The United States has two centers that monitor, detect, and issue warnings for tsunamis. The National Oceanic and Atmospheric Administration's (NOAA's) National Weather Service (NWS) manages both centers. The NWS operates the Pacific Tsunami Warning Center (PTWC) at Ford Island, Hawaii, and the National Tsunami Warning Center (NTWC) at Palmer, Alaska. (Before October 1, 2013, the NTWC was known as the West Coast and Alaska Tsunami Warning Center, or WC/ATWC). The PTWC monitors for tsunamis and issues warnings for the Hawaiian Islands, the U.S. Pacific territories, and other U.S. and international interests in the Pacific basin outside the NTWC area of responsibility. Following the 2004 Indian Ocean tsunami, the PTWC took on responsibility for monitoring the Indian Ocean, South China Sea, Caribbean Sea, and, temporarily, the U.S. Virgin Islands and Puerto Rico (until June 2007, when responsibility was passed to what was then known as the WC/ATWC). The PTWC was established in 1949 after a strong earthquake and massive landslides off the coast of Southwest Alaska caused a disastrous tsunami that hit the Hawaiian Islands only hours later. The PTWC issued tsunami warnings to Alaska until 1967, when the WC/ATWC was established. The WC/ATWC (now the NTWC) was established in the aftermath of the magnitude 9.2 Good Friday earthquake that struck Anchorage, Alaska, in 1964 and caused major earthquake and localized tsunami damage. The NTWC is responsible for issuing tsunami warnings to emergency management officials in Alaska, British Columbia (Canada), Washington State, Oregon, and California. In 2005, the NTWC expanded its scope to include the U.S. Atlantic and Gulf of Mexico coasts, as well as the Atlantic coast of Canada. In 2007, the NTWC added Puerto Rico and the U.S. and British Virgin Islands to its scope. Figure 1 shows the areas of responsibility for the PTWC and the NTWC. The tsunami warning centers monitor and evaluate data from seismic networks and determine if a tsunami is likely based on the location, magnitude, and depth of an earthquake. If a center determines that a tsunami is likely, it transmits a warning message to NOAA's weather forecasting offices and state emergency management centers, as well as to other recipients. The centers monitor coastal water-level data, typically with tide-level gauges, and data from NOAA's network of Deep-Ocean Assessment and Reporting of Tsunamis (DART) detection buoys to confirm that a tsunami has been generated or, if one has not been generated, to cancel any warnings. Figure 2 shows a generalized decision tree network for the earthquake-detection-through-warning process. NOAA first completed a six-buoy DART array in 2001 in the Pacific Ocean. After the 2004 Indian Ocean earthquake and tsunami that killed more than 200,000 people, Congress passed P.L. 109-424 , the Tsunami Warning and Education Act, to enhance and modernize the existing Pacific Tsunami Warning System and broaden coverage, reduce false alarms, and increase the accuracy of forecasts and warnings, among other purposes. In part, the 2004 tsunami provided the impetus to expand and upgrade the DART system and to improve the U.S. capability to detect and issue warnings for tsunamis generally. As a result, the DART array was expanded to a total of 39 U.S. DART buoys in March 2008. (See Figure 3 .) In addition, 8 other countries operate 21 additional DART buoys positioned near faults in the seafloor beneath the Indian and Pacific Oceans, bringing the global total to 60 buoys. P.L. 109-424 requires that NWS ensure that maintaining operations of tsunami detection equipment is the highest priority within the tsunami forecasting and warning program at NOAA. Further, P.L. 109-424 requires the NOAA administrator to notify Congress within 30 days of (1) impaired regional forecasting capabilities due to equipment or system failures and (2) significant contractor failures or delays in completing work associated with the tsunami forecasting and warning system. As of November 18, 2015, 4 of the 39 U.S. buoys (10%) were not operational. This represents an improvement over the course of the year; in March 2015, 9 of the buoys were not operational (23%). The inoperable stations likely would not prevent the issuance of tsunami warnings, which are primarily a function of seismic data from an earthquake or landslide, combined with location information about the event. However, lacking stations could mean the warnings encompass a larger area than would be the case if all stations were operating, and it could lengthen the time a warning remains in effect. According to NOAA, the National Tsunami Hazard Mitigation Program (NTHMP) was formed in response to the recognition of a tsunami threat to Oregon, Washington State, and Northern California from a large earthquake on the Cascadia subduction zone, which lies off the northwest coast of the United States and is capable of generating earthquakes as large as magnitude 9 or greater. Among other activities, the NTHMP assists states in emergency planning and in developing maps of potential coastal inundation for a tsunami of a given intensity. The NTHMP also operates tsunami disaster outreach and education programs in support of NOAA's TsunamiReady program. NOAA's primary goals for the NTHMP are as follows: 1. raise awareness of the affected population; 2. develop integrated tsunami maps and recognize models that can be used to develop improved warning guidance and evacuation maps; 3. improve tsunami warning systems; and 4. incorporate tsunami planning into state and federal multi-hazard programs. The Tsunami Warning and Education Act, P.L. 109-424 , further focused the NTHMP and charged NOAA with addressing the nation's priorities in tsunami detection, warning, and mitigation. As authorized by P.L. 109-424 , the NTHMP assumed responsibility for planning and executing NOAA's tsunami activities, namely detection, warning, forecasts, communication, outreach and education, and research. The program coordinates activities among NOAA organizational entities and outside partners. Maintenance and availability of the DART buoy network have been key issues for Congress. In its report accompanying the FY2015 Commerce, Justice, Science, and Related Agencies appropriations bill, the House Appropriations Committee admonished NOAA for failing to maintain its network to its own 80% availability standard, despite receiving full funding in FY2014. In P.L. 109-424 , Congress stated that "maintaining operational tsunami detection equipment is the highest priority within the program carried out under this Act." This requirement also was included in a Senate bill ( S. 2181 ) that would have reauthorized the tsunami program in the 113 th Congress. In the 114 th Congress, bills introduced in the House ( H.R. 34 ) and Senate ( S. 533 ) address DART buoy maintenance and availability as well as other issues regarding the NTHMP. The House passed H.R. 34 , the Tsunami Warning, Education, and Research Act of 2015, on January 7, 2015, by unanimous consent. The Senate passed its version of the legislation, as an amendment in the nature of a substitute for H.R. 34 , on October 6, 2015, by unanimous consent. The following section provides a brief comparison of the bills. Both versions of the legislation would amend the Tsunami Warning and Education Act and authorize appropriations for the NTHMP through FY2017 ( H.R. 34 ) or through FY2021 ( S. 533 ). Authorization for the program's appropriations in P.L. 109-424 expired in FY2012. Both bills apparently would not make fundamental changes to the NTHMP but would broaden the program to include an additional focus on tsunami research and outreach, among other alterations. The following summarizes the changes the House- and Senate-passed bills would make to P.L. 109-424 on a section-by-section basis and notes significant differences between the two versions. Except where noted, the discussion refers to specific sections of the proposed legislation and not to sections of current law. Both bills would add the term research to the title of the act. P.L. 109-424 defined NOAA and the NOAA administrator . Both bills would omit the section on definitions. Both bills would streamline and update the language in several subsections and add a new subsection (4) that focuses on research as part of the program: "to improve research efforts related to improving tsunami detection, forecasting, warnings, notification, mitigation, resiliency, response, outreach, and recovery." Both bills are broadly similar throughout Section 4, with some important distinctions. Both bills would streamline and update the language in several subsections. In subsection (b), the Senate-passed version would require that 80% of the DART buoys be maintained at operational capacity. It also would include a requirement for a cooperative effort among NOAA, the U.S. Geological Survey, and the National Science Foundation under which the agencies' directors would "provide rapid and reliable seismic information ... from international and domestic seismic networks." The House-passed bill does not include those provisions. Both bills would rename subsection (c) the Tsunami Warning System (previously System Areas). This subsection would require the system to be capable of forecasting tsunamis in the Pacific, Arctic, and Atlantic Oceans, including the Caribbean Sea and Gulf of Mexico. Subsection (c) also would require a system that supports other international forecasting and warning efforts.