Strength and Structure of the EarthPDF电子书下载

1. INTRODUCTORY 1

The Problem 1

Vocabulary 5

Discontinuities in the Earth 16

Calculated Internal Densities 21

Figure of the Earth; Geoid, Ellipsoid, Spheroid 24

2. DEVELOPMENT OF THE IDEA OF ISOSTASY 36

Bouguer to Petit 36

Pr 38

Airy 42

Hall 50

Jamieson 50

Dutton 51

Gilbert 53

Helmert ; Schweydar 54

Suggestions Regarding Isostatic Compensation 56

3. TESTING ISOSTASY WITH THE PLUMB-LINE 65

Deflections of the Vertical 65

Hayford's First Investigation 67

Topographic Deflections 70

Construction of the Geoid 78

Recognition of Isostasy 81

Effect of Isostatic Compensation on the Direction of the Vertical 87

Statistical Tests of Conclusions 94

Degree of Isostatic Compensation 99

Amended Ellipsoid of Reference 102

Hayford's Second Investigation 102

Conclusions Regarding the Dimensions of Uncompensated Loads 104

4. MEASUREMENT OF GRAVITY; COMPARISON OF INTENSITIES 106

Gravitation 106

Relation of Gravity to Latitude 109

Measurement of Gravity 111

Reduction of Values of Gravity 114

Free-air Reduction 114

Bouguer Reduction 116

Isostatic Reductions 120

Indirect Reduction 126

Clearing-house for Systematic Record of Anomalies 129

5. GRAVIMETRIC TESTS OF ISOSTASY IN THE UNITED STATES, BY HAYFORD AND BOWIE 131

Introduction 131

Assumed Conditions for Isostatic Compensation 132

Theoretical Gravity at a Station 139

Correction for Elevation 139

Correction for the Effects of Topography and Compensation 140

Specimen Isostatic Anomalies 149

Comparison with the Corresponding Free-air and Bouguer Anomalies 149

Local Versus Regional Compensation 152

Relation of Anomaly to Varying Depth of Compensation 154

Anomalies in Terms of Masses 154

General Conclusions 156

6. LATER GRAVIMETRIC TESTS OF ISOSTASY IN NORTH AMERICA 159

Bowie Report of 1912 159

Bowie Report of 1917 161

Bowie Report of 1924 174

United States Values of Gravity Reported Since 1924 182

Putnam's Discussion of United States Data 184

Gilbert's Estimate of Uncompensated Loads 187

Heiskanen on Gravity in the United States 187

Gravity in Canada 190

Concluding Remarks 191

7. TESTING ISOSTASY IN EUROPE 196

Introduction 196

Gravity in Alps and Apennines 197

Heiskanen's Studies 205

Caucasus 205

Norway 208

Gravity in Finland 210

Gravity Measurements in Cyprus 211

Additional European Data 213

Review and Forecast 215

8. TESTING ISOSTASY IN AFRICA AND ASIA 218

Earlier Work in East Africa 218

Bullard on Gravity in East Africa 219

Gravity in Siberia 224

Conditions in India 224

The Geoid in India 225

Gravity Anomalies in India 236

Observations in Turkestan 247

Gravity Anomalies in Japan 248

Some Leading Results 250

9. TESTING ISOSTASY AT SEA 252

Introduction 252

Observations of Hansen, Schi?tz, and Hecker 253

Measurement of Gravity at Sea, by Vening Meinesz 256

Mean Gravity Anomalies Over the Open Ocean 259

Gravity Anomalies Over Mediterranean Seas 264

Strip of Negative Anomalies, East Indies 269

Negative Strip of the West Indies 285

Anomalies Over Ocean Deeps Facing Mountainarcs 290

Gravity Profiles off Shores 294

Gravity Anomalies in the Vicinity of Volcanic Islands 298

Gravity Anomalies at Stations Near Great Deltas 303

Conclusions 305

10. NATURE'S EXPERIMENTS WITH ICECAPS 309

Introduction 309

Jamieson Hypothesis 310

Warping of Fennoscandia, Past and Present 312

Objections to Jamieson's Isostatic Hypothesis 316

Recoil of the Glaciated Tract of Northeastern North America 326

Nansen's Evidence from the Strandflat 330

Summary 334

11. RETROSPECT 337

Introduction 337

Meaning of the Word "Isostasy" 338

Proofs of Close Approach of the Earth to Ideal Isostasy 342

Relation of Gravity Anomaly to Spheroid of Reference 344

Need of Great Extension of the Gravitational Survey 345

Effect of Errors of Mensuration and Computation 348

Effect of Changing the Assumed Type of Isostatic Compensation 349

Effect of Changing the Assumed Depth of Compensation 350

Effect of Local Abnormalities of Density of Rock 351

How Permanent are Areas of One-sign Anomaly? 351

12. STRENGTH OF THE EARTH-SHELLS 353

Introduction 353

Stresses Caused by Departures from Isostasy 355

Dimensions of Stable Areas of One-sign Anomaly 361

Anomaly Areas in the United States 362

Mechanical Conditions in Peninsular India 364

Anomaly Field Along the Pacific Coast of North America 369

Anomaly Field of the Eastern Atlantic and Adjacent Land 371

Anomaly Field of the Western Pacific 373

Summary 373

Anomaly Fields of the Mediterranean Seas 373

Anomaly Fields of the Open-ocean "Deeps" 376

Anomaly Fields Surrounding Volcanic Islands 379

Comparison of Loads on Continental and Oceanic Sectors; Strength of the Lithosphere 380

Experiments on the Relation of High Confining Pressure to the Strength of Rock 384

The Unstable Glaciated Tracts 385

Comparison of Conditions in India and Fennoscandia 390

Horizontal Variation of Thickness of the Lithosphere 393

Strength of the Lithosphere at Earlier Geological Epochs 396

The Asthenosphere and Theories of Diastrophism and Petrogenesis 398

The Asthenosphere and Deep-focus Earthquakes 400

The Asthenosphere and Warped Peneplains 407

Strength of the Mesospheric Shell 408

Conclusions 410

INDEX 419