地震中に屋外でやるべきこと: 屋外安全

Walking or Standing: Move to Open Ground

When shaking begins while you are on foot outdoors, your primary objective is to reach open ground away from all structures, trees, and overhead infrastructure within ten seconds. Move away from buildings, which shed glass, facade tiles, and structural components during 震度人・構造物・自然環境への観測された影響から判定される、特定地点における揺れの強さの尺度。震央からの距離が離れるほど小さくなる。 VII or above shaking. A falling facade panel or glass sheet is lethal, and the danger zone extends outward approximately one-quarter of the building's height in all directions.

Once you have cleared the immediate building hazard zone, drop to your hands and knees. Open ground gives you visibility in all directions and eliminates the risk of toppling from loss of balance. Protect your head and neck with your arms and remain on the ground until all shaking has completely stopped. 「まず低く、頭を守り、動かない」（Drop, Cover, and Hold On）地震の揺れの最中に国際的に推奨される防護行動。両手と両膝をつき、頑丈な家具の下に隠れ、揺れが収まるまでその姿勢を保つ。 applies outdoors as much as indoors; the "hold" element becomes covering your head with your arms when no table is available.

After shaking stops, assess the ground surface before rising. Cracks in pavement, lateral displacement of sidewalk sections, and wet ground that was previously dry are signs of soil failure. Move away from cracked ground, storm drains, and retaining walls, as subsurface damage may continue to develop in the minutes following the mainshock. Be alert to 余震本震と同じ断層領域で本震の後に続く、より規模の小さい地震。余震活動は数週間から数年続くことがあり、最大の余震は通常本震よりマグニチュードが1.0〜1.2小さい。 sequences, which may begin within seconds of the mainshock ending.

Driving: Pull Over Safely

If you are driving when shaking begins, you may not immediately distinguish earthquake ground motion from a blown tire or road irregularity. The distinguishing characteristic of earthquake shaking is that it affects all vehicles simultaneously and the road surface itself appears to be moving. When you identify earthquake shaking, reduce speed immediately, pull to the right, and stop away from buildings, bridges, overpasses, trees, and power lines.

Stay inside your vehicle during shaking. The vehicle provides a protective cage against most falling debris, and exiting the vehicle during shaking risks being knocked down by ground motion or struck by a moving or skidding vehicle. After shaking stops, check the road ahead before proceeding. Bridge and overpass 二次的地震災害揺れそのものではなく、揺れによって引き起こされる災害——津波・地すべり・液状化・火災・ダム決壊・化学物質の流出などを指す。揺れそのものより大きな被害をもたらすことが多い。 include abutment cracking, deck displacement, and structural failure; do not proceed across a bridge without visual confirmation that the deck is intact.

If you are stopped under an overpass when shaking begins, do not exit the vehicle and shelter under the overpass structure. This advice from pre-1994 guidance has been retracted; the 1994 Northridge earthquake collapsed several overpasses, and the confined space beneath an overpass offers no protection against a falling deck. If your vehicle is positioned under an overpass, drive forward or backward to clear the structure before stopping.

Near Buildings: Falling Debris Dangers

The hazard zone adjacent to multistory buildings during strong shaking is defined by the distance that facade materials can travel when dislodged. Unreinforced parapet walls — the low walls above rooflines common in pre-1940s commercial buildings — are notorious failure points that project debris outward at speed. 無補強組積造（URM）鉄筋補強のないレンガまたはブロック造の建物で、地震の揺れに極めて脆弱である。URM建物は、世界の地震死者数の大部分を占める。 buildings can shed entire wall sections during shaking greater than intensity VII. The safe distance from a 10-story building is at minimum 30 feet; for older masonry construction, double this estimate.

Glass curtain walls on modern commercial buildings present a different profile: the glass itself is typically laminated safety glass that fractures into small pieces rather than large sheets, but the entire window unit including frame can fail as an assembly during severe racking of the building frame. Move perpendicular to the building face to exit the fall zone rather than running parallel to the facade where you remain exposed throughout the run.

After shaking stops, do not re-enter buildings until they have been assessed by structural engineers or building officials. Many earthquake casualties occur during re-entry to structurally compromised buildings, either because of continuing damage from 余震本震と同じ断層領域で本震の後に続く、より規模の小さい地震。余震活動は数週間から数年続くことがあり、最大の余震は通常本震よりマグニチュードが1.0〜1.2小さい。 sequences or because of interior hazards not visible from the exterior. Wait for official clearance, particularly for older buildings or those showing visible cracking.

At the Beach: Tsunami Evacuation

If you feel strong, prolonged shaking while at or near the coast, treat it as a 津波海底地震時の海底の急激な変位によって発生する一連の海の波。津波はジェット機並みの速度（時速700km以上）で海洋全域を伝わることがある。 warning and evacuate immediately to high ground — do not wait for an official warning. The largest tsunamis arrive within minutes of the generating earthquake in near-field scenarios, and the time to reach the 津波避難区域津波による浸水リスクがあり、高台への避難経路が示された指定区域。沿岸部で強い揺れを感じたら、直ちに避難を開始すべきである。 boundary may be less than fifteen minutes. Natural warning signs — the unusual retreat of water from the beach, a loud roaring sound from the ocean, or an unusual wave — indicate that the first tsunami wave is imminent.

Move inland and uphill as rapidly as possible. A minimum elevation of 100 feet above sea level provides protection from most tsunami scenarios, but large subduction-zone events such as a Cascadia Subduction Zone rupture can generate runup exceeding 100 feet in topographically focused areas. If you cannot reach high ground in time, the upper floors of a steel-reinforced concrete building may provide 屋内待避（シェルター・イン・プレイス）地震時または地震後に避難するのではなく、現在の場所にとどまる行動。建物が構造的に健全で、津波の危険がない場合に適切な対応である。 protection as a vertical evacuation refuge.

Never return to the beach after the first wave has passed. Tsunami 二次的地震災害揺れそのものではなく、揺れによって引き起こされる災害——津波・地すべり・液状化・火災・ダム決壊・化学物質の流出などを指す。揺れそのものより大きな被害をもたらすことが多い。 include multiple waves over a period of several hours, with the first wave often smaller than subsequent arrivals. The sea will appear to recede again between waves, which triggers fatal re-entry by people who believe the event is over. Official all-clear announcements from the Pacific Tsunami Warning Center or equivalent authority are the only reliable signal that it is safe to return to coastal areas.

In the Mountains: Landslide Risk

Strong earthquake shaking destabilizes slopes by reducing the effective friction between soil and rock layers, triggering 地震誘発地すべり地震の揺れによって引き起こされる、土砂や岩石の斜面下方への移動。地すべりは地域全体を埋没させることがあり、揺れそのものより多くの犠牲者を出すこともある。 events at distances far from the epicenter. The risk is highest on steep slopes with loose soils, slopes that have been recently burned in wildfires, and slopes already saturated by rainfall. When shaking begins in mountainous terrain, immediately assess your position relative to upslope terrain and move to flat ground or solid rock outcrops if possible.

A 地震誘発地すべり地震の揺れによって引き起こされる、土砂や岩石の斜面下方への移動。地すべりは地域全体を埋没させることがあり、揺れそのものより多くの犠牲者を出すこともある。 triggered by earthquake shaking may begin during the shaking itself or in the minutes to hours following the mainshock as residual vibration propagates through saturated soils. If you hear cracking sounds in trees, see dust rising from slopes above you, or observe water and debris beginning to flow on previously dry slopes, move laterally across the slope rather than down the fall line. Lateral movement takes you out of the primary debris path; running downhill puts you ahead of fast-moving debris for only the seconds before the flow accelerates.

After shaking stops, do not assume that mountain roads are passable. Rock falls, road collapse, and bridge damage are common on mountain highways after significant earthquakes. Wait at a safe assembly point for official assessment of road conditions before attempting to drive out of mountainous terrain.

Bridges, Overpasses, and Tunnels

Bridge and overpass structures in the United States are designed to varying seismic standards depending on their construction date and jurisdiction. Pre-1971 structures in California and pre-1975 structures in most other western states were designed without modern seismic requirements and carry elevated collapse risk during strong shaking. If you are on a bridge or overpass when shaking begins, move to the nearest open roadway off the structure as quickly as safely possible.

If you are in a tunnel when shaking begins, pull over safely, stay in your vehicle, and protect yourself from falling materials. Modern mountain and highway tunnels are generally among the most seismically resilient structures because the surrounding rock constrains movement, but older cut-and-cover tunnels in urban areas can experience portal collapse and internal cracking. Do not exit your vehicle in an unlit, debris-strewn tunnel environment; wait for emergency response or official guidance before proceeding.

After a large earthquake, assume all bridges and overpasses should be inspected before use. Route around bridge structures if alternate surface roads are available. Use Distance from Epicenter to assess how close your location is to the estimated epicenter and calibrate your expectations for infrastructure damage accordingly.