USGS地震地図の使用方法

Getting Started with the USGS Earthquake Map

The アメリカ地質調査所（USGS）地震の監視、National Earthquake Information Centerの運用、世界の地震データのリアルタイム公開を担う、アメリカ政府の主要機関。 Earthquake Hazards Program operates one of the world's most comprehensive public earthquake monitoring platforms. At earthquake.usgs.gov, anyone can access real-time data from thousands of seismic stations, explore historical records stretching back decades, and visualize 地震観測網地震活動を継続的に監視する、連携した地震観測点の集合。世界地震観測網（GSN）は150以上の観測点から構成され、世界規模の観測範囲を提供する。 data through an interactive map interface. Understanding how to navigate this tool effectively transforms raw seismological data into actionable information.

The Live Earthquake Feed

When you first open the USGS earthquake map, you are viewing a live feed that updates continuously. Each colored circle represents an earthquake, with size indicating マグニチュード地震が放出した総エネルギー量を表す単一の数値。整数値が1増えるごとに、放出エネルギーはおよそ31.6倍になる。 and color indicating how recently the event occurred. By default the map shows events from the past day, but dropdown menus let you expand the view to the past week, past month, or past 30 days. Filters along the top bar allow you to restrict results by magnitude threshold, which is useful for filtering out the constant low-level microseismicity that occurs worldwide every hour.

Decoding the Color and Size Legend

The magnitude-size relationship on the USGS map is logarithmic, reflecting the actual energy scale. A circle representing a magnitude 6.0 event is not simply twice as large as one for a magnitude 5.0 — the area difference is far greater, corresponding to the roughly 32-fold difference in energy release between each whole-number step. Color coding shifts from green (very recent) through yellow and orange to red (older events within the selected window), allowing rapid visual identification of the freshest activity.

Clicking Into an Event

Clicking any circle opens a pop-up with essential data: マグニチュード地震が放出した総エネルギー量を表す単一の数値。整数値が1増えるごとに、放出エネルギーはおよそ31.6倍になる。, depth, location description, and time. Following the link to the full event page reveals far more detail. The event page displays the 地震記象（地震波形記録）地震計が記録した出力で、地面の揺れを時間の関数として示したもの。地震学者はこの記録を解析し、地震の規模・深さ・位置を求める。 recorded at nearby stations, a map showing the 震央地下で地震が発生した震源の真上にあたる地表の地点。ニュース報道では地震の発生場所としてよく報じられる。, and shake data contributed by citizens through the 「揺れを感じましたか？」（DYFI）地震後に一般市民から震度に関する報告を収集し、市民参加型の震度マップを作成するUSGSのプログラム。地震を感じた誰もが報告を投稿できる。 program. The ANSS Comprehensive Earthquake Catalog (ComCat) entry is also accessible, providing the authoritative record that researchers cite in published studies.

Using the Earthquake Calculator Tool

When reviewing an event on the USGS map, the Earthquake Energy Calculator tool complements the official data by letting you compute derived quantities. Enter the magnitude to see estimated energy release in joules, equivalent TNT tonnage, and moment magnitude equivalents. This contextualization helps translate abstract numbers into understandable comparisons.

Navigating the Settings Panel

The settings gear icon on the USGS map opens a panel with advanced filtering controls. You can toggle tectonic plate boundaries, historic seismicity density overlays, and fault line layers simultaneously. Overlaying 断層線地表に現れた断層の痕跡で、線状または破砕された岩石の帯として視認できる。地質学者は活断層線を地図化し、周辺地域の地震リスクを評価する。 data with recent seismicity is particularly illuminating in regions like California, Japan, and Türkiye, where individual events visibly cluster along known structures.

Earthquake Notification Setup

The USGS offers free email and push notification subscriptions through their Earthquake Notification Service. You can configure alerts for specific geographic regions, magnitude thresholds, and depth ranges. Setting up notifications for your home region at M 3.0 or above gives you awareness of moderate local activity without overwhelming alert fatigue from global micro-earthquakes.

Understanding Location Uncertainty

Every USGS earthquake location carries an uncertainty estimate, reported as horizontal and vertical uncertainty in kilometers. Events near dense 地震観測網地震活動を継続的に監視する、連携した地震観測点の集合。世界地震観測網（GSN）は150以上の観測点から構成され、世界規模の観測範囲を提供する。 coverage — such as those in California served by the California Integrated Seismic Network — have horizontal uncertainties under one kilometer. Events in remote ocean areas may have uncertainties of tens of kilometers because the nearest stations are far away. The depth estimate is typically less certain than the horizontal location, especially for shallow events where the waveform timing differences between stations are subtle.

Historical Search and the ANSS ComCat

The ComCat query interface allows filtering by date range, bounding box, depth, and magnitude. Researchers use it to study 地震クラスタリング地震がランダムに発生するのではなく、本震・余震系列や群発地震のようにクラスター（集団）として発生する傾向。地震が独立してランダムに発生するという一般的な仮定に反する。, 地震空白域隣接する区間と比較して、長期間にわたり地震が発生していない活断層の区間。地震空白域は、将来の地震発生確率が高いことを示唆する場合がある。 identification, and b値グーテンベルク・リヒターの頻度・マグニチュード関係の傾きを表す値。1.0前後が一般的で、値が高いほど大地震に対して小地震の割合が多いことを示す。値の変化は応力状態の変化を示唆することがある。 analysis. For the general public, a useful application is searching historical events near a prospective home or business location to understand long-term seismicity patterns. Export options include CSV, GeoJSON, and QuakeML for further analysis.

Interpreting Aftershock Sequences

When a significant earthquake occurs, the USGS map makes the ensuing 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。 sequence visible in near real time. Zooming into the affected region and selecting the past week will show the mainshock plus dozens or hundreds of aftershocks forming a spatially coherent cluster. This cluster typically outlines the ruptured 断層セグメント特有のすべり挙動を持つ、より大きな断層系の中の明確な区間。異なるセグメントが独立して、あるいは連鎖的に破壊することがあり、地震の規模に影響する。. The decay of aftershock frequency over time follows 大森公式（オモリ則）時間経過に伴う余震発生頻度の減衰を示す経験則で、余震の発生率は本震からの経過時間にほぼ反比例して減少する。, and the USGS publishes operational aftershock forecasts that quantify expected activity in the days and weeks ahead.

Contributed Citizen Reports

The Did You Feel It? (DYFI) system integrates directly with the earthquake map. After any felt event, a link on the event page invites you to report your experience using a standardized questionnaire. Your responses contribute to a community 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。 map that supplements instrumental data. In areas with few seismic stations, citizen reports may be the primary data source for mapping felt shaking extent, making DYFI contributions scientifically valuable.

Accessing Raw Waveform Data

For those with seismological training, the USGS Earthquake Map links to waveform archives through IRIS (now EarthScope). Raw seismic waveforms in SEED format can be downloaded for any catalogued event, enabling custom analysis using tools like ObsPy. The USGS also provides moment tensor solutions for earthquakes above roughly M 3.5, which describe the fault geometry and slip direction of the event.

Summary

The USGS earthquake map is a gateway to the 世界地震観測網（GSN）世界の地震活動を包括的に監視する、150以上の広帯域地震観測点からなる世界規模のネットワーク。USGS・NSF・IRISが共同で運用している。 and its decades of archived data. By learning to filter events, interpret uncertainty estimates, layer tectonic context, and access underlying data, you move from passive observer to active analyst. Whether your interest is immediate situational awareness, property risk evaluation, or scientific research, the platform provides a free and continuously maintained resource of exceptional depth.