Heatmap Earthquakes

<!--
  说明：地震热力图
  核心逻辑：ol.layer.Heatmap 用震级作 weight，滑块调节 blur 与 radius
  依赖：OpenLayers 10.3.1 · jsDelivr CDN
-->
<!DOCTYPE html>
<html lang="zh-CN">
<head>
<meta name="robots" content="noindex,follow">
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<title>地震热力图</title>
<link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/ol@10.3.1/ol.css">
<style>
  html,body{height:100%;margin:0}
  body{display:flex;flex-direction:column;overflow:hidden;
       font:13px/1.6 -apple-system,"Segoe UI","PingFang SC",sans-serif}
  .bar{flex:0 0 auto;padding:8px 12px;background:#f6f7f9;border-bottom:1px solid #e3e6ea;
       display:flex;gap:12px;align-items:center;font-size:12px;color:#58606e;flex-wrap:wrap}
  .bar input[type=range]{width:120px}
  #info{margin-left:auto}
  #map{flex:1 1 auto;min-height:0;background:#eef0f3}
</style>
</head>
<body>
<div class="bar">
  <label><input type="checkbox" id="tgl" checked> 热力层</label>
  <label>模糊 <input type="range" id="blur" min="5" max="40" step="1" value="18"></label>
  <label>半径 <input type="range" id="radius" min="4" max="30" step="1" value="12"></label>
  <span id="info">—</span>
</div>
<div id="map"></div>
<script src="https://cdn.jsdelivr.net/npm/ol@10.3.1/dist/ol.js"></script>
<script>
(function () {
  'use strict';

  if (typeof ol === 'undefined') {
    document.getElementById('map').innerHTML =
      '<div style="padding:20px;color:#b42318">OpenLayers 加载失败，请检查能否访问 cdn.jsdelivr.net</div>';
    return;
  }

  var fromLonLat = ol.proj.fromLonLat;

  var source = new ol.source.Vector();
  var feats = [];
  for (var i = 0; i < 500; i++) {
    var lon = 100 + Math.random() * 22;
    var lat = 24 + Math.random() * 16;
    var f = new ol.Feature({ geometry: new ol.geom.Point(fromLonLat([lon, lat])) });
    f.set('mag', 2 + Math.random() * 4.5);
    feats.push(f);
  }
  source.addFeatures(feats);

  var heat = new ol.layer.Heatmap({
    source: source,
    blur: 18,
    radius: 12,
    weight: function (feature) {
      return feature.get('mag') / 6.5;
    },
    gradient: ['#2c5aa0', '#39a0a8', '#c9d34a', '#e06a3b', '#c8281c']
  });

  var view = new ol.View({ center: fromLonLat([111, 32]), zoom: 4, minZoom: 2, maxZoom: 19 });

  var map = new ol.Map({
    target: 'map',
    layers: [new ol.layer.Tile({ source: new ol.source.XYZ({url: 'https://server.arcgisonline.com/ArcGIS/rest/services/World_Street_Map/MapServer/tile/{z}/{y}/{x}', attributions: 'Tiles © Esri'}) }), heat],
    view: view,
    controls: ol.control.defaults.defaults({ attribution: false, rotate: false })
  });

  var info = document.getElementById('info');

  document.getElementById('tgl').addEventListener('change', function () {
    heat.setVisible(this.checked);
  });

  document.getElementById('blur').addEventListener('input', function () {
    heat.setBlur(Number(this.value));
    info.textContent = '模糊 ' + this.value + ' px · 半径 ' + heat.getRadius() + ' px';
  });

  document.getElementById('radius').addEventListener('input', function () {
    heat.setRadius(Number(this.value));
    info.textContent = '模糊 ' + heat.getBlur() + ' px · 半径 ' + this.value + ' px';
  });

  info.textContent = '500 个震中 · 模糊 18 px · 半径 12 px';
})();
</script>
</body>
</html>