reference sea level The observed elevation differences between geodetic bench marks are processed through least-squares adjustments to determine orthometric heights referred to a common vertical reference surface, which is the reference sea level. In this way, height values of all bench marks in the vertical control portion of a surveying agency are made consistent and can be compared directly to determine differences of elevation between bench marks in a geodetic reference system that may not be directly connected by lines of geodetic leveling. The vertical reference surface in use in the United States, as in most parts of the world, approximates the geoid. The geoid was as sumed to be coincident with local mean sea level at 26 tidal stations to obtain the Sea Level Datum of 1929 (SLD 290). National Geodetic Vertical Datum of 1929 (NGVD 29) became a name change only; the same vertical reference system has been in use in the United States since 1929. This important vertical geodetic control system is made possible by a universally accepted, reference sea level.

regional tsunami A tsunami capable of destruction in aparticular geographic region, generally with in about 1000 km of its source. Regional tsunamis also occasionally have very limited and localized effects outside the region. Most destructive tsunami can be classified as local or regional, meaning their destructive effects are confined to coasts within a hundred km, or up to a thousand km, respectively, of the source -- usually an earthquake. It follows that the majority of tsunami related casualties and property damage also come from local tsunami. Between 1975 and 1998 there have been at least eighteen in the Pacific and its adjacent seas resulting in significant casualties and/or property damage. For example, a regional tsunami in 1983 in the Sea of Japan or East Sea, severely damaged coastal areas of Japan, Korea, and Russia, causing more than $800 million in damage, and more than a hundred deaths. Then, after nine years without an event, eleven locally destructive tsunamis occurred in just a seven-year period from 1992 to 1998, resulting in over 4,200 deaths and hundreds of millions of dollars in property damage. In most of these cases, tsunami mitigation efforts in place at the time were unable to prevent significant damage and loss of life. However, losses from future local or regional tsunamis can be reduced if a denser network of warning centers, seismic and water-level reporting stations, and better communications are established to provide a timely warning, and if better programs of tsunami preparedness and education can be put in place.

Regional Tsunami Warning/Watch Bulletin Message issued initially by PTWC based only on seismic information to alert all participants of the possibility of a tsunami and advise them that a tsunami investigation is underway. Those areas that are within 0 to 3 hours from the estimated time of arrival of the first wave are placed in a Tsunami Warning status. Those areas within 3 to 6 hours are placed in a Tsunami Watch status. It will be followed by additional bulletins until it is either upgraded to a Pacific-wide Tsunami Warning or until it is cancelled. The following is an example of a Regional Warning/Watch Bulletin issued by the PTWC. TSUNAMI BULLETIN NUMBER 001 PACIFIC TSUNAMI WARNING CENTER/NOAA/NWS ISSUED 13 JAN,1808 UTC   THIS BULLETIN IS FOR ALL AREAS OF THE PACIFIC BASIN EXCEPT CALIFORNIA, OREGON, WASHINGTON, BRITISH COLUMBIA, AND ALAS-KA. ...A TSUNAMI WARNING AND WATCH ARE IN EFFECT ... A TSUNAMI WARNING IS IN EFFECT FOR: NICARAGUA, ELSALVADOR, MEXICO A TSUNAMI WATCH IS IN EFFECT FOR: ECUADOR, PANAMA, PERU   FOR OTHER AREAS IN THE PACIFIC, THIS MESSAGE IS FOR INFORMATION ONLY.   AN EARTHQUAKE, PRELIMINARY MAGNITUDE 7.7, OCCURRED 13 JAN,1733 UTC. COORDINATES: LATITUDE 13.1 NORTH, LONGITUDE 88.6 WEST VICINITY: OFF COAST OF CENTRAL AMERICA. EVALUATION: IT IS NOT KNOWN THAT A TSUNAMI WAS GENERATED. THIS WARNING AND WATCH ARE BASED ONLY ON EARTHQUAKE EVALUATION.   ESTIMATED TIMES OF INITIAL WAVE ARRIVAL AT LOCATIONS WITHIN THE WARNING AND WATCH AREAS ARE: NICARAGUA CORINTO 1946Z 13 JAN   PUERTO SANDINO 1947Z 13 JAN   SAN JUAN DL SUR 2025Z 13 JAN EL SALVADOR ACAJUTLA 1955Z 13 JAN MEXICO ACAPULCO 2034Z 13 JAN   MANZANILLO 2133Z 13 JAN   SOCORRO 2219Z 13 JAN ECUADOR BALTRA IS. 2115Z 13 JAN PANAMA BALBOA HTS. 2247Z 13 JAN PERU LA PUNTA 2343Z 13 JAN BULLETINS WILL BE ISSUED HOURLY OR SOONER IF CONDITIONS WARRANT.   THE TSUNAMI WARNING WILL REMAIN IN EFFECT UNTIL FURTHER NOTICE.   RECIPIENTS OF THIS MESSAGE LOCATED IN CALIFORNIA, OREGON, WASHINGTON, BRITISH COLUMBIA, AND ALASKA SHOULD REFER ONLY TO ALASKA TSUNAMI WARNING CENTER MESSAGES FOR INFORMATION ABOUT ANY TSUNAMI THREAT IN THOSE AREAS.

Regional Tsunami Warning/Watch Bulletin Message issued initially by PTWC based only on seismic information to alert all participants of the possibility of a tsunami and advise them that a tsunami investigation is underway. Those areas that are within 0 to 3 hours from the estimated time of arrival of the first wave are placed in a Tsunami Warning status. Those areas within 3 to 6 hours are placed in a Tsunami Watch status. It will be followed by additional bulletins until it is either upgraded to a Pacific-wide Tsunami Warning or until it is cancelled. The following is an example of a Regional Warning/Watch Bulletin issued by the PTWC. TSUNAMI BULLETIN NUMBER 001 PACIFIC TSUNAMI WARNING CENTER/NOAA/NWS ISSUED 13 JAN,1808 UTC   THIS BULLETIN IS FOR ALL AREAS OF THE PACIFIC BASIN EXCEPT CALIFORNIA, OREGON, WASHINGTON, BRITISH COLUMBIA, AND ALAS-KA. ...A TSUNAMI WARNING AND WATCH ARE IN EFFECT ... A TSUNAMI WARNING IS IN EFFECT FOR: NICARAGUA, ELSALVADOR, MEXICO A TSUNAMI WATCH IS IN EFFECT FOR: ECUADOR, PANAMA, PERU   FOR OTHER AREAS IN THE PACIFIC, THIS MESSAGE IS FOR INFORMATION ONLY.   AN EARTHQUAKE, PRELIMINARY MAGNITUDE 7.7, OCCURRED 13 JAN,1733 UTC. COORDINATES: LATITUDE 13.1 NORTH, LONGITUDE 88.6 WEST VICINITY: OFF COAST OF CENTRAL AMERICA. EVALUATION: IT IS NOT KNOWN THAT A TSUNAMI WAS GENERATED. THIS WARNING AND WATCH ARE BASED ONLY ON EARTHQUAKE EVALUATION.   ESTIMATED TIMES OF INITIAL WAVE ARRIVAL AT LOCATIONS WITHIN THE WARNING AND WATCH AREAS ARE: NICARAGUA CORINTO 1946Z 13 JAN   PUERTO SANDINO 1947Z 13 JAN   SAN JUAN DL SUR 2025Z 13 JAN EL SALVADOR ACAJUTLA 1955Z 13 JAN MEXICO ACAPULCO 2034Z 13 JAN   MANZANILLO 2133Z 13 JAN   SOCORRO 2219Z 13 JAN ECUADOR BALTRA IS. 2115Z 13 JAN PANAMA BALBOA HTS. 2247Z 13 JAN PERU LA PUNTA 2343Z 13 JAN BULLETINS WILL BE ISSUED HOURLY OR SOONER IF CONDITIONS WARRANT.   THE TSUNAMI WARNING WILL REMAIN IN EFFECT UNTIL FURTHER NOTICE.   RECIPIENTS OF THIS MESSAGE LOCATED IN CALIFORNIA, OREGON, WASHINGTON, BRITISH COLUMBIA, AND ALASKA SHOULD REFER ONLY TO ALASKA TSUNAMI WARNING CENTER MESSAGES FOR INFORMATION ABOUT ANY TSUNAMI THREAT IN THOSE AREAS.

rise The upward change or elevation in sea level associated with a tsunami, a hurricane, a tide, or some long term climatic effect.

run-up 1. Difference between the elevation of maximum tsunami penetration (inundation line) and the sea-level at the time of the tsunami attack. 2. Elevation reached by seawater measured relative to some stated datum such as mean sea level, mean low water, sea level at the time of the tsunami attack, etc., and measured ideally at a point that is a local maximum of the horizontal inundation. 3. In practical terms, run-up is only measured where there is a clear evidence of the inundation limit on the shore. Tsunami termination cross-section view

run-up distribution Set of tsunami runup values measured or observed along a coastline. Run-up measured during the Hokkaido Nansei Tsunami of July, 12, 1993.