쓰나미 위험 추정기

Estimate tsunami risk based on earthquake parameters and your coastal proximity.

Assessment

지진이 쓰나미를 생성하는 원리

쓰나미는 갑작스러운 대규모 해수 변위에 의해 발생하는 해양파로, 가장 일반적으로 섭입대를 따른 해저 지진에 의해 발생합니다. 대규모 지진 중에 해양 지각의 일부가 위로 솟아오르거나 아래로 떨어지면, 방대한 양의 물이 변위되어 일련의 장주기파로 외부로 전파됩니다. 심해에서 쓰나미파는 500~800 km/h(제트기와 유사)의 속도로 이동하며 파고는 30~60 cm에 불과하여 거의 감지할 수 없습니다. 파도가 얕은 해안 수역에 접근하면 속도가 줄고 압축되어 파고가 극적으로 증폭됩니다. 이를 천수 효과(shoaling)라 하며, 해안선에서 10~30미터 이상에 달할 수 있습니다.

모든 지진이 쓰나미를 발생시키지는 않습니다. 핵심 요소는: 지진이 해저(바다 아래)에서 발생해야 하며, 얕아야 하고(통상 70 km 미만), 대규모여야 하며(지역 쓰나미의 경우 일반적으로 M7.0 이상, 광역 쓰나미는 M7.5+), 해저의 상당한 수직 변위를 수반해야 합니다. 주로 수평적 단층 운동을 수반하는 주향이동 단층 지진은 심각한 쓰나미를 거의 발생시키지 않습니다. 가장 위험한 쓰나미 발생 메커니즘은 섭입대 메가스러스트의 역단층 운동으로, 2004년 인도양(M9.1), 2011년 도호쿠(M9.1), 1960년 칠레(M9.5) 지진에서 잘 나타납니다.

쓰나미 과학의 핵심 개념

쓰나미 경보 시간은 거리에 따라 달라집니다: 근거리 쓰나미는 10~30분 내에 도달할 수 있으며, 대양 횡단 쓰나미는 몇 시간이 걸릴 수 있습니다. 2011년 일본 쓰나미는 22시간 후 칠레에 도달했습니다.
쓰나미 지진은 규모에 비해 불균형적으로 큰 쓰나미를 발생시키는 느린 파열 사건의 특수한 유형으로, 인근 해안에 특히 위험합니다.
처오름 높이 — 육지에서 물이 도달하는 최대 수직 높이 — 는 해안 지형과 항만 공진 효과로 인해 해상 파고를 크게 초과할 수 있습니다.
태평양쓰나미경보센터(PTWC)와 지역 경보 센터는 DART 부이(심해 압력 센서)를 사용하여 쓰나미를 실시간으로 감지하고 확인합니다.

일반적인 용도

보고된 지진이 매개변수를 기반으로 쓰나미를 발생시킬 가능성이 있는지 이해.
지진 특성과 쓰나미 발생 간의 관계에 대한 교육적 탐구.
여행 또는 이전 계획을 위한 해안의 쓰나미 위험 노출 평가.
쓰나미 경보 시스템과 근거리 사건에 대한 즉각적 대피의 중요성에 대해 학습.

How to Use

1
Enter Earthquake Parameters
Input the earthquake magnitude, focal depth, and location. Tsunamis are most efficiently generated by shallow (< 50 km depth) thrust earthquakes with vertical fault displacement; the tool checks these criteria automatically.
2
Specify Your Coastal Location
Enter your coastal city or coordinates. The tool calculates your approximate distance from the source and identifies whether you are in a mapped tsunami inundation zone based on NOAA and national tsunami center data.
3
Read Your Risk Summary
Review the estimated wave arrival time, indicative wave height range, and evacuation tier. Treat all outputs as supplementary to official warnings from PTWC, NTHMP, or JMA, which must always take precedence.

About

Tsunami science sits at the intersection of seismology, physical oceanography, and coastal engineering. The word tsunami derives from the Japanese 津波 (tsu, harbor; nami, wave), reflecting Japan's millennia of devastating experience with these events. Despite their colloquial name 'tidal waves,' tsunamis have no connection to tidal forces; they are long-period gravity waves with wavelengths of 100–500 km in deep water and wave periods of 10–60 minutes, compared to wind-driven ocean waves with periods of seconds.

The physics of tsunami generation requires a mechanism that displaces a large volume of water vertically over a large area. Megathrust earthquakes accomplish this by the sudden elastic rebound of the overriding plate—the 2011 Tohoku earthquake caused the seafloor to rise by 5–8 meters over a 300 × 200 km area instantaneously, displacing an estimated 5 cubic kilometers of water. The resulting wave system propagates radially, with energy concentrated perpendicular to the fault strike. Directivity effects mean that the coast directly opposite the rupture typically receives the highest waves.

The Deep-ocean Assessment and Reporting of Tsunamis (DART) buoy network, operated primarily by NOAA, provides real-time sea-level measurements from the deep ocean floor. These buoys detect tsunami wave amplitudes of centimeters in the open ocean, enabling confirmation or cancellation of warnings within 15–30 minutes of a potentially tsunamigenic earthquake. Combined with coastal tide gauge networks and numerical propagation models, DART data allows warning centers to issue probabilistic wave height forecasts for coastal communities hours before wave arrival in distant-field scenarios. Local and regional tsunamis remain the most challenging problem in warning science because the lead times are measured in minutes.

FAQ

What earthquakes generate tsunamis?

Tsunamis are most commonly generated by shallow (< 50 km depth) submarine thrust earthquakes that produce significant vertical seafloor displacement, typically exceeding 1 meter over large areas. The key factors are: magnitude ≥ M7.5 (though some M7.0 events with favorable geometry have generated destructive tsunamis), a thrust (reverse) or oblique-thrust focal mechanism with a large vertical displacement component, shallow focal depth in the crust or uppermost mantle, and occurrence beneath ocean floor rather than continental crust. Strike-slip earthquakes—where motion is primarily horizontal, as on transform faults—rarely generate significant tsunamis. The 2018 Sulawesi earthquake was exceptional: a predominantly strike-slip event triggered localized submarine landslides that generated the devastating Palu Bay tsunami.

How fast do tsunamis travel and when do they arrive?

Tsunami propagation speed in open ocean is governed by the shallow-water wave formula: v = √(g × d), where g is gravitational acceleration and d is ocean depth. In the deep Pacific (average depth ~4,000 m), tsunamis travel at approximately 700–800 km/h—comparable to a commercial jet aircraft. As waves enter shallower coastal water, they slow dramatically (to 50–100 km/h near shore) while their amplitude increases through shoaling. This means a tsunami generated 4,000 km away arrives in about 5–6 hours in deep water, but can take 30–60 minutes to inundate a coast after entering shallow shelf waters. The Pacific Tsunami Warning Center (PTWC) issues initial bulletins within 3 minutes of detecting a significant seismic event.

How far inland can tsunami waves travel?

Tsunami inundation distance depends on wave height, coastal topography, and land elevation. The 2011 Tohoku tsunami waves reached heights of 40.5 m (at Miyako, Japan) and inundated up to 10 km inland across flat coastal plains, destroying the town of Rikuzentakata. In contrast, mountainous coastlines confine inundation to narrow strips. Maximum inundation run-up is generally defined as the highest elevation reached by wave water, measured as meters above mean sea level. NOAA and national emergency management agencies have mapped tsunami inundation zones for high-risk coastlines using numerical models calibrated against historical events. These maps define evacuation zones (A through E or Zone 1 through 3 depending on jurisdiction) for emergency planning.

Is a tsunami warning always issued after a large earthquake?

Warning centers issue tsunami warnings, advisories, and watches based on rapid seismic analysis within minutes of a significant event. PTWC monitors earthquakes globally and issues initial bulletins for any event M7.0+ in ocean basin settings within 3 minutes. However, the first message is often a 'tsunami information statement' that may not indicate confirmed wave generation—definitive warnings come after sea-level gauges and DART buoys confirm or deny wave propagation. Local tsunamis—generated by earthquakes within 50–100 km of shore—can arrive within 5–20 minutes, before official warnings are disseminated. In these cases, the natural warning is the shaking itself: the international standard guidance is that prolonged strong shaking near the coast (> 20 seconds) is itself a tsunami warning signal, and coastal residents should evacuate immediately without waiting for official messages.

Are there tsunamis caused by non-earthquake sources?

Tsunamis can be generated by submarine landslides, volcanic activity, meteorite impacts, and atmospheric pressure disturbances (meteotsunamis). Submarine landslides are the second most common cause: the 1958 Lituya Bay event in Alaska, triggered by an earthquake-induced rockslide, produced a 524-meter run-up—the tallest wave in recorded history. The 2022 Hunga Tonga-Hunga Ha'apai volcanic eruption generated an unusual meteotsunami-like pressure wave that propagated globally at the speed of sound in the atmosphere (~340 m/s), reaching Peru and Japan within hours. Volcanic island collapses—hypothesized for the Canary Islands—could theoretically generate Atlantic basin tsunamis, though the probability and magnitude of such events are debated in the scientific community.