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Chapter IS:Risk Assessment <br /> POSSIBLE <br /> TSUNAMI <br /> -•450mph <br /> y 0-0 TIDE GAUGE <br /> �0 }D 7Mf7f� GROUND WAVE SEISMOGRAPH <br /> 5m" <br /> EARTHOVAKE � <br /> CHECK S REPORTS DES IS <br /> REPORTS OUT MAG?77 <br /> 6 PTWC IN W/ETA WATCH 3 <br /> 5mm. NO <br /> ■ ESS IGNORE <br /> lnl 7 <br /> DECISION YES <br /> CIVIL EVAC- ? <br /> TSUNAMI? DEFENSE UATION <br /> NO 3hr <br /> CANCEL SIRENS <br /> WATCH <br /> Tsunami Warning System Flow Chart <br /> HOW DOES THE <br /> TSUNAMI WARNING SYSTEM <br /> WORK? <br /> When a significant earthqualae(1)occurs in the Pacific,it is detected(2)at the <br /> Pacific Tsunami Warning Center(PTWC)in Ewa Beach,Oahu. Five geophysicists <br /> man the Center around the clock. If the magnitude I'3)is greater than 7,the <br /> epicenter is located. If the epicenter is in an area lilzely to cause a tsunami,a <br /> tsunami warning{a is sent to nearby coasts and a tsunami watch is set for areas <br /> with a travel time more than three hours away. Messages are sent to tide <br /> observers for a report on the first wave,(S)and telemetered water level gages <br /> are checlaed. In addition,the earthquahe's moment is calculated. The <br /> geophysicists(S)quickly review the earthquake and sea level data and historical <br /> information to decide if a warning is needed for areas currently under a watch <br /> condition. If hazardous waves are predicted(7),the warning is sent to <br /> emergency officials across the Pacific at least three hours ahead of the first wave <br /> (the speed of the waves has been pre-calculated for all areas). People can then <br /> be cleared from all coastal areas(S)that might be hit by the waves. I <br /> Red numbers correspond to numbers on the Tsunami Warning 5ystem Flow Chart <br /> Figure 18-7. Pacific Tsunami Warning System <br /> • Flooding(rainfall, high waves) and Hurricanes--National Weather Service Forecast Office <br /> (NWS) <br /> • Lava flow--Hawaiian Volcano Observatory,U.S. Geological Survey <br /> The warnings from the PTWC and NWS are issued as a "watch" and/or a "warning" to the <br /> County Civil Defense Agency. <br /> The Civil Defense activates the sirens to alert people to seek further information from the ra- <br /> dio or TV. The Civil Defense transmits warnings to the public through the Emergency Alert <br /> System, which consists of simultaneous broadcasts over all radio and television stations. An <br /> 18-21 Hawaii County Multi-Hazard Mitigation Plan <br />